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2015-2022 Volkswagen Touran 4 Door Air conditioning system -> 2.14 Checking pressures User Manual

MY CAR USER MANUAL

Air conditioning system -> 2.14 Checking pressures for Your Volkswagen Touran 4 Door Second Generation (2015-2022)

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ Sealed recycling cylinders from your gas supplier usually  
come pre-evacuated.  
♦ Should the recycling cylinder not be evacuated, evacuate it as  
necessary using a vacuum pump or an air conditioner service  
station .  
♦ Recycling cylinders are clearly marked as such and, unlike  
refrigerant cylinders, do not have a non-return valve thereby  
making them suitable for filling.  
♦ Recycling cylinders are designed for international use, which  
is why the “O” on the handwheel means “Open” (cylinder valve  
= open) and not “0” (zero = closed).  
♦ If an absolute pressure greater than 100 mbar but less than  
900 mbar is measured in the recycling cylinder, evacuate the  
recycling cylinder using a vacuum pump (or an air conditioner  
service station ) (residual pressure less than 50 mbar)  
⇒ “2.5 Evacuating refrigerant circuit”, page 140 .  
♦ If an absolute pressure greater than 900 mbar is measured in  
the recycling cylinder, this could be due to a number of rea‐  
sons. The manual shut-off valve was opened and not closed  
properly or the recycling cylinder had previously been used to  
store refrigerant and then was not evacuated properly  
⇒ “2.10 Emptying air conditioner service station”, page 154  
(evacuate recycling cylinder). The recycling cylinder is leaking  
(return the recycling cylinder to the supplier).  
lk  
– Connect a vacuum metre (or air conditioner service station )  
to the recycling cylinder.  
– Carefully open the manual shut-off valve of the recycling cyl‐  
inder to check the vacuum and then check the vacuum in the  
cylinder.  
– If necessary, evacuate the recycling cylinder with the air con‐  
ditioner service station .  
Note  
♦ Should there be any air trapped in the recycling cylinder, it can  
be evacuated using an air conditioner service station for  
R1234yf. To do this, unscrew the low pressure service cou‐  
pling from the charge hose of the air conditioner service station  
and connect the charge hose directly to the recycling cylinder  
adapter for the extraction device (for R1234yf refrigerant) - dry  
ice box .  
♦ If air is trapped in the recycling cylinder and there is no air  
conditioner service station for R1234yf available, the recycling  
cylinder can also be evacuated with an air conditioner service  
station for R134a using a relevant flushing container and  
adapter -VAS 6338/38- along with the charge hose from ex‐  
traction device (for R1234yf refrigerant) - dry ice box .  
•
Residual pressure in the recycling cylinder less than 10 mbar  
absolute pressure.  
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Note  
♦ Recycling cylinders are pre-evacuated by the supplier, though  
it is not always possible to ensure that the vacuum will remain  
intact in storage.  
♦ To reliably determine the type and scope of the contamination  
of the refilled refrigerant during analysis of the contaminated  
refrigerant, the recycling cylinder must be evacuated before  
refilling to a residual pressure less than 50 mbar.  
– Switch off ignition.  
– Ensure that the workplace is well ventilated. Switch on addi‐  
tional workshop extraction systems if fitted.  
– Connect the charge hose with a suitable adapter to the evac‐  
uated recycling cylinder.  
CAUTION  
Risk of explosion from overfilling refrigerant reservoirs.  
Refrigerant can expand and cause reservoirs to burst if they are  
overfilled.  
– Use a refrigerant tank with safety valve.  
– Never exceed the permissible fill level of the refrigerant tank.  
lk  
Note  
♦ Since contaminated refrigerant is only filled into a recycling  
cylinder from a vehicle in the following work routine, there is  
no danger of a recycling cylinder being overfilled with a fill vol‐  
ume exceeding 3.0 kg.  
♦ If contaminated refrigerant is filled into a recycling cylinder e.g.  
from an air conditioner service station , measures must be  
taken to ensure that the recycling cylinder is not overfilled due  
to the larger volume. Use a recycling cylinder with an appro‐  
priate permissible fill capacity and when refilling ensure by  
means of weighing that the maximum permissible fill volume  
is not exceeded.  
CAUTION  
Chemical reactions from contaminated refrigerant. Mixing  
gases of unknown composition can cause different chemical  
reactions.  
Risk of injuries.  
– Never mix together refrigerants of different origins.  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
– Connect the service coupling for R1234yf refrigerant -5- to the  
charge hose -4-.  
– Connect the charge hose -4- with cylinder adapter -3- (and  
seal -2-) to the recycling cylinder -1-.  
– Place the spacer -6- in the insulated container -7-.  
– Cover the base of the insulated container -7- with dry ice.  
– Place the recycling cylinder -1- in the insulated container -7-  
extraction device (for R1234yf refrigerant) - dry ice box .  
– Pour the remainder of the dry ice in the insulated container  
-7-.  
– Cool down the recycling container -1- with dry ice (for approx.  
15 minutes).  
– Connect the recycling cylinder -1- via the service coupling  
-5- to the connection of the air conditioner service station (or  
the vehicle's refrigerant circuit).  
– Open the manual shut-off valve of the recycling cylinder -1-.  
Note  
Recycling cylinders are designed for international use, which is  
why the “O” on the handwheel means “Open” (cylinder valve =  
open) and not “0” (zero = closed).  
– Connect a pressure gauge to the refrigerant circuit (or use the  
pressure gauge of the air conditioner service station ) and  
check the pressure in the refrigerant circuit.  
– Carefully open the service coupling -5- on the charge hose for  
the recycling cylinder and allow the refrigerant to flow out  
slowly into the recycling cylinder -1-.  
– Wait until the refrigerant in the recycling cylinder -1- has liq‐  
uefied (watch the display on the connected pressure gauge).  
Note  
♦ You can use your own pressure gauge or the pressure gauge  
of the air conditioner service station to monitor the extraction  
process.  
♦ As soon as the displayed pressure is less than 0.3 bar after  
approx. 60 minutes, it is safe to assume that the whole refrig‐  
erant in the recycling cylinder is liquefied.  
♦ Complete evaporation of the contaminated refrigerant from the  
refrigerant circuit takes some time. After 60 minutes, it is safe  
to assume that the whole refrigerant has evaporated.  
– Close the service coupling -5- and manual shut-off valve of the  
recycling cylinder -1-.  
– Remove the charge hose -4- and cylinder connecting piece  
-3- from the recycling cylinder -1- and close the recycling cyl‐  
inder with the cap.  
– The paperwork required for analysis, processing (or disposal)  
of contaminated refrigerant must be filled in completely (dis‐  
posal record, acceptance certificate etc.).  
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Note  
♦ All of the information and documents for analysis, processing  
(or disposal) can be obtained from your gas processing / gas  
disposal company.  
♦ Included with the recycling cylinder is a form. Kindly fill this in  
accordingly and attach it to the recycling cylinder.  
♦ If it is not possible to weigh the recycling cylinder before and  
after filling with contaminated refrigerant, the fill volume speci‐  
fied for the vehicle in question can be quoted as the amount  
of refrigerant that was filled in the recycling cylinder. This is  
permissible as only the amount of refrigerant from a vehicle is  
filled in a recycling cylinder.  
– Move the insulated box -7- with recycling cylinder -1- and dry  
ice to a secure, well ventilated area outside the building.  
– Open the lid of the insulated box -7- or remove and allow the  
dry ice to evaporate.  
Note  
Do not take the recycling cylinder -1- out of the insulated container  
-7- until the dry ice has evaporated and the recycling cylinder has  
adjusted to ambient temperature.  
– Remove the recycling cylinder -1- from the insulated container  
-7-.  
lk  
– Take the recycling cylinder -1- to a suitable location for storage  
until it is ready to be collected by the gas processing / gas  
disposal company.  
– Evacuate the refrigerant circuit with the air conditioner service  
station for at least 1 hour  
⇒ “2.5 Evacuating refrigerant circuit”, page 140 .  
Note  
♦ Subsequent evacuation results in the last remnants of conta‐  
minated refrigerant, which could still be in the refrigerant oil,  
being removed at an absolute pressure of less than 10 mbar.  
♦ The next steps depend on the complaint with the refrigerant  
circuit  
⇒ “2.3 Performing gas analysis of refrigerant”, page 134 .  
– Fill out the data sheet for the recycling cylinder (R-cylinder) if  
the refrigerant is contaminated and firmly attach it to the recy‐  
cling cylinder -1-.  
Note  
In the “Other comments” section, details can be provided regard‐  
ing e.g. who is to receive the analysis results and in which way.  
Example for recycling cylinder (R-cylinder) data sheet  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Data sheet for R-cylinder if refrigerant is contaminated  
Service contact  
Dealership contact:  
Email address:  
Customer information:  
Surname, first name:  
Street:  
Town/city:  
Vehicle model  
Identification  
Vehicle identification  
number:  
Mileage:  
Gas analysis performed  
on:  
Information about R-cylinder  
Cylinder number:  
Cylinder weight with  
contents:  
(gross weight)  
Fill volume  
(net weight)  
lk  
Other comments  
2.14  
Checking pressures  
⇒ “2.14.1 General information on checking pressures in the re‐  
frigerant circuit”, page 170  
⇒ “2.14.2 Pressures and temperatures in refrigerant circuit”, page  
173  
⇒ “2.14.3 Checking pressures in the refrigerant circuit with the  
ignition switched off”, page 176  
⇒ “2.14.4 Checking pressures with air conditioning system switch‐  
ed on - vehicles with mechanical air conditioning compressor”,  
page 183 .  
⇒ “2.14.5 Checking pressures with air conditioning system switch‐  
ed on - vehicles with electrical air conditioning compressor”, page  
205  
2.14.1  
General information on checking pres‐  
sures in the refrigerant circuit  
Note  
Work on the refrigerant circuit that involves the air conditioner  
service station can usually be carried out without the need to de-  
energise the high-voltage system.  
170  
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Vehicles with electrically-actuated valves in the refrigerant circuit  
that are not open when de-energised:  
lk  
Note  
On vehicles with high-voltage system and auxiliary air condition‐  
ing system functions (“heat pump mode” or “cooling of high-  
voltage battery”), valves may be installed in the refrigerant circuit  
that are not open when de-energised. These valves are opened  
and closed e.g. via incremental motors and are no longer actu‐  
ated when the ignition is switched off. To check the pressures in  
the refrigerant circuit with the air conditioning system switched off,  
however, no areas may be isolated, which is why these valves  
must be opened before work is carried out ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit; System overview -  
refrigerant circuit and ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
– Use the vehicle diagnostic tester to open the electrically-ac‐  
tuated valves that are not open when de-energised ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode.  
All vehicles  
NOTICE  
Risk of damage to the air conditioner compressor or air condi‐  
tioner service station.  
Opening the valves with the air conditioning system switched  
on can cause a short circuit between the high pressure and low  
pressure side.  
– Never open valves on the high pressure or low pressure side  
with the air conditioning system switched on.  
Note  
♦ Certain conditions for testing are pertinent to a certain vehicle  
and are described in the vehicle-specific workshop manual ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output .  
♦ Check the cooling output ⇒ Heating, air conditioning; Rep. gr.  
00 ; Repair instructions; Checking cooling output (vehicle-spe‐  
cific workshop manual).  
♦ Connections with valve and service connections for measuring  
and testing ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit; System overview - refrigerant circuit (vehicle-  
specific workshop manual)  
♦ Depending on the version of air conditioner compressor, a  
valve may be installed on the high-pressure side that prevents  
liquefied refrigerant flowing back into the air conditioner com‐  
pressor after the air conditioning system is switched off. If an  
air conditioner compressor with this valve is installed in a ve‐  
hicle with a refrigerant circuit with expansion valve, it could  
take some time before the pressure on the high-pressure side  
drops (the expansion valve is cold and the pressure on the  
low-pressure side rises quickly after switching off, the expan‐  
sion valve closes and refrigerant only flows slowly on the low-  
pressure side). If the air conditioner compressor is switched  
on, the pressure on the low-pressure side drops, the expan‐  
sion valve opens and refrigerant can flow on the low-pressure  
side.  
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Under certain operating conditions, residual moisture in the re‐  
frigerant circuit may lead to the formation of ice at the air condi‐  
tioner compressor regulating valve. The ice impairs the air  
conditioner compressor control and causes the evaporator to be  
cooled excessively and to ice up. Icing-up of the evaporator may  
give rise to the following problems:  
♦ Repeated or sporadic failure of the air conditioner (no cooling/  
heat output) after a lengthy journey. After switching off the en‐  
gine and waiting for a short period, operation of air conditioner  
returns to normal.  
♦ Misting up of the windows on the inside after a long journey;  
the windows are initially not cleared even by pressing the De-  
frost button; the air conditioner functions properly again after  
a short delay following engine shut-off (or after switching off  
the air conditioner).  
Remedy:  
– On vehicles with an air conditioner compressor with air con‐  
ditioner compressor regulating valve - N280- , check the  
measured value of the evaporator output temperature sender  
- G263- (via the “Read measured values” function). If the  
measured value of the sender is too low under the operating  
conditions described by the customer (at an ambient temper‐  
ature above 0°C, colder than 0°C for an extended period even  
though the -N280- is currently not actuated) or too high (higher  
than approx. 10°C, even though the air conditioning system is  
lk  
functioning properly): the evaporator may ice up due to the  
incorrect measured value ⇒ Vehicle diagnostic tester in “Gui‐  
ded Fault Finding” mode - air conditioning system and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual).  
– On vehicles without evaporator output temperature sender -  
G263- , use e.g. the footwell vent temperature sender - G192-  
to check the outlet temperature with the temperature set to  
“low” or “cold” for the driver and front passenger side with the  
lowest setting (4 or 5 bars) for the fresh air blower speed, air  
outlet in the footwell and fresh air mode under the operating  
conditions described by the customer. If the measured value  
of the sender is too low (with an ambient temperature higher  
than 0°C, colder than 0°C for an extended period), the evap‐  
orator could ice up due to the wrong measured value ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air condi‐  
tioning system.  
– On vehicles with shut-off valves in the refrigerant circuit, check  
the function and actuation of these valves ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode - air conditioning sys‐  
tem, ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit; System overview - refrigerant circuit and ⇒ Heating,  
air conditioning; Rep. gr. 00 ; Repair instructions; Checking  
cooling output (vehicle-specific workshop manual).  
– Check the refrigerant line from the evaporator (or from the in‐  
ner heat exchanger) and the air conditioner compressor (thick  
pipe, low pressure side) with the engine running. If this line is  
very icy when the complaint is encountered (a thin layer of ice  
is acceptable), this is also evidence that the temperature in the  
evaporator is too low ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit; System overview - refrigerant circuit (vehi‐  
cle-specific workshop manual).  
– Empty the refrigerant circuit, renew the receiver with dryer,  
renew the reservoir with dryer or desiccant cartridge and then  
evacuate the refrigerant circuit for at least 3 hours ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit; System over‐  
view - refrigerant circuit (vehicle-specific workshop manual)  
and ⇒ page 129 .  
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♦ ⇒ “2.14.3 Checking pressures in the refrigerant circuit with the  
ignition switched off”, page 176  
♦ ⇒ “2.14.4 Checking pressures with air conditioning system  
switched on - vehicles with mechanical air conditioning com‐  
pressor”, page 183 .  
♦ ⇒ “2.14.5 Checking pressures with air conditioning system  
switched on - vehicles with electrical air conditioning com‐  
pressor”, page 205  
2.14.2  
Pressures and temperatures in refriger‐  
ant circuit  
General information about pressures and temperatures in the re‐  
frigerant circuit ⇒ page 173  
Pressures and temperatures in refrigerant circuit with expansion  
valve ⇒ page 174  
General information about pressures and temperatures in the re‐  
frigerant circuit  
♦ The pressures and temperatures in the refrigerant circuit de‐  
pend on the current operating conditions (e.g. engine speed,  
radiator running at level 1, 2, or 3, engine temperature, air  
conditioner compressor actuation on or off) as well as envi‐  
ronmental influences (e.g. ambient temperature, humidity, re‐  
quired cooling output).  
♦ On vehicles with air conditioner compressor regulating valve -  
N280- , the pressure on the low pressure side is varied by  
means of -N280- actuation.  
lk  
♦ For these reasons, the values given in the following table may  
only be considered guidelines. They occur at an engine speed  
of 1,500 to 2,000 rpm and an ambient temperature of 20°C  
after about 20 minutes.  
♦ Refer to the vehicle-specific refrigerant circuit for the pressure  
gauge set measurement connections ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific work‐  
shop manual).  
♦ At 20°C and with the engine stationary, the refrigerant circuit  
will adjust itself to a pressure of 4.7 bar overpressure  
⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17 (va‐  
pour pressure table).  
Note  
♦ Pressure is indicated in various units: 1 MPa (Mega-Pascal)  
is equal to 10 bar or 145 psi; 1 bar absolute pressure is equal  
to 0 bar, which is about the same as ambient pressure (at‐  
mospheric pressure).  
♦ The pressures and temperatures in refrigerant circuits with re‐  
strictor and reservoir are about the same as those in refriger‐  
ant circuits with expansion valve. Since Volkswagen/Audi  
currently only installs refrigerant circuits with expansion valve,  
just this refrigerant circuit is described here.  
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Pressures and temperatures in refrigerant circuit with expansion  
valve  
Note  
♦ The following log (p), h-diagram (logarithmic pressure, energy  
diagram) shows the processes that run during certain operat‐  
ing conditions in the refrigerant circuit. These values change  
depending on the environmental conditions (engine speed,  
ambient temperature, requisite cooling output, etc.).  
♦ The log (p), h-diagram shows the pressure (0 to 60 in bar ab‐  
solute pressure) and the energy content (100 to 420, specific  
enthalpy in kilojoules per kg of R1234yf refrigerant) in the re‐  
frigerant circuit cycle.  
lk  
♦ The arrows indicate the direction of refrigerant flow in the re‐  
frigerant circuit.  
A - Area with vaporous refrigerant  
B - Area with gaseous refrigerant  
C - Area with liquefied refrigerant  
D - Supercritical pressure and temperature range, physical state  
of refrigerant undetermined (no longer a separation between liq‐  
uefied and gaseous refrigerant)  
1 - Low pressure side: output of inner heat exchanger, input of  
air conditioner compressor, refrigerant is completely evapo‐  
rated and gaseous, temperature of refrigerant is approx. -4°  
C
2 - High pressure side: output of air conditioner compressor,  
input of condenser, refrigerant has been compressed and is  
gaseous, temperature of refrigerant is up to approx. 80°C  
3 - High pressure side: output of condenser (receiver), input of  
inner heat exchanger, refrigerant has been cooled down and  
is liquefied, temperature of refrigerant is approx. 55°C  
4 - High pressure side: output of inner heat exchanger, input of  
expansion valve, liquefied refrigerant has cooled down fur‐  
ther, temperature of refrigerant is approx. 50°C  
5 - Low pressure side: expansion valve on evaporator side, in‐  
put of evaporator, liquefied refrigerant comes to rest and  
starts to evaporate, temperature of refrigerant approx. -7°C  
6 - Low pressure side: output of evaporator, expansion valve,  
input of inner heat exchanger, refrigerant mainly evapora‐  
ted, small percentage is still vaporous, temperature of re‐  
frigerant approx. -6°C  
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Note  
lk  
♦ The temperatures given relate to the refrigerant in the refrig‐  
erant circuit. The temperatures deviate from this on the sur‐  
face of components containing refrigerant owing to heat  
absorption and dissipation.  
♦ The pressure and the temperature, too, are maintained at ap‐  
prox. 3 bar absolute pressure (equates to approx. 2 bar over‐  
pressure) in refrigerant circuits with regulated air conditioner  
compressor despite thermal changes and different engine  
speeds. This applies however only within the rated range of  
the air conditioner compressor; if the rated range of the air  
conditioner compressor is exceeded, the pressure will in‐  
crease and so, too, will the temperature  
⇒ “2.14 Checking pressures”, page 170 .  
♦ On air conditioner compressors that do not regulate their per‐  
formance themselves, the pressure on the low pressure side  
and thereby the evaporator temperature are regulated by the  
respective control via the air conditioner compressor regulat‐  
ing valve - N280- . Depending on the version and the setting,  
if an air temperature of less than approx. 2°C is measured after  
the evaporator, the performance of the air conditioner com‐  
pressor is lowered. At below 0°C, -N280- actuation is switched  
off. This prevents the evaporator from cooling down too much  
and becoming icy.  
♦ On vehicles with two evaporators and two expansion valves,  
the temperature and pressure in the refrigerant circuit are the  
same at the second evaporator as those in vehicles with only  
one evaporator and one expansion valve (parallel circuit).  
♦ Depending on the version of refrigerant circuit, a component  
with inner heat exchanger may be installed. In the internal heat  
exchanger, the hot liquid refrigerant flowing on the high pres‐  
sure side supplies energy to the cold gaseous or vaporous  
refrigerant flowing on the low pressure side, thus enhancing  
the efficiency of the air conditioner  
⇒ “1.2.13 Refrigerant line with internal heat exchanger”, page  
51 .  
♦ Depending on the version of control unit (e.g. operating and  
display unit for front air conditioning system - E87- or Clima‐  
tronic control unit - J255- ), the measured ambient conditions  
(exterior temperature, moisture in the passenger compartment  
etc.) and the control unit setting (passenger compartment tem‐  
perature, operating mode etc.), the pressure and thereby also  
the temperature at the output of the evaporator can also be  
regulated at a higher temperature ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system.  
2. Working with air conditioner service station  
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2.14.3  
Checking pressures in the refrigerant  
circuit with the ignition switched off  
Test prerequisites ⇒ page 176  
Checking pressures with the ignition switched off ⇒ page 179  
Conditions for testing  
Note  
♦ Work on the refrigerant circuit that involves the air conditioner  
service station (checking the pressures in this case) can usu‐  
ally be carried out without the need to de-energise the high-  
voltage system.  
♦ Only de-energise the high-voltage system if work on the high-  
voltage system is necessary ⇒ page 3  
All vehicles  
Note  
♦ Certain conditions for testing are pertinent to a certain vehicle  
and are described in the vehicle-specific workshop manual ⇒ lk  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual).  
♦ Depending on the version of air conditioner compressor, a  
valve may be installed on the high-pressure side that prevents  
liquefied refrigerant flowing back into the air conditioner com‐  
pressor after the air conditioning system is switched off. If an  
air conditioner compressor with this valve is installed in a ve‐  
hicle with a refrigerant circuit with expansion valve, it could  
take some time before the pressure on the high-pressure side  
drops (the expansion valve is cold and the pressure on the  
low-pressure side rises quickly after switching off, the expan‐  
sion valve closes and refrigerant only flows slowly on the low-  
pressure side). If the air conditioner compressor is switched  
on, the pressure on the low-pressure side drops, the expan‐  
sion valve opens and refrigerant can flow on the low-pressure  
side.  
♦ Check the cooling output ⇒ Heating, air conditioning; Rep. gr.  
00 ; Repair instructions; Checking cooling output (vehicle-spe‐  
cific workshop manual).  
♦ Connections with valve and service connections for measuring  
and testing ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
♦ Connect the air conditioner service station  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
Under certain operating conditions, residual moisture in the re‐  
frigerant circuit may lead to the formation of ice at the air condi‐  
tioner compressor regulating valve. The ice impairs the air  
conditioner compressor control and causes the evaporator to be  
cooled excessively and to ice up. Icing-up of the evaporator may  
give rise to the following problems:  
♦ Repeated or sporadic failure of the air conditioner (no cooling/  
heat output) after a lengthy journey. After switching off the en‐  
gine and waiting for a short period, operation of air conditioner  
returns to normal.  
176  
Rep. gr.87 - Air conditioning system  
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♦ Misting up of the windows on the inside after a long journey;  
the windows are initially not cleared even by pressing the De-  
frost button; the air conditioner functions properly again after  
a short delay following engine shut-off (or after switching off  
the air conditioner).  
Remedy:  
– On vehicles with an air conditioner compressor with air con‐  
ditioner compressor regulating valve - N280- ,lkcheck the  
measured value of the evaporator output temperature sender  
- G263- (via the “Read measured values” function). If the  
measured value of the sender is too low under the operating  
conditions described by the customer (at an ambient temper‐  
ature above 0°C, colder than 0°C for an extended period even  
though the -N280- is currently not actuated) or too high (higher  
than approx. 10°C, even though the air conditioning system is  
functioning properly): the evaporator may ice up due to incor‐  
rect actuation of -N280- or the incorrect measured value of -  
G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system and ⇒ Heating, air condition‐  
ing; Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific workshop manual).  
– On vehicles without evaporator output temperature sender -  
G263- , use e.g. the footwell vent temperature sender - G192-  
to check the outlet temperature with the temperature set to  
“low” or “cold” for the driver and front passenger side with the  
lowest setting (4 or 5 bars) for the fresh air blower speed, air  
outlet in the footwell and fresh air mode under the operating  
conditions described by the customer. If the measured value  
of the sender is too low (with an ambient temperature higher  
than 0°C, colder than 0°C for an extended period), the evap‐  
orator could ice up due to the wrong measured value ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air condi‐  
tioning system.  
– On vehicles with shut-off valves in the refrigerant circuit, check  
the function and actuation of these valves ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode - air conditioning system  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific workshop manual).  
– Check the refrigerant line from the evaporator (or from the in‐  
ner heat exchanger) and the air conditioner compressor (thick  
pipe, low pressure side) with the engine running. If this line is  
very icy when the complaint is encountered (a thin layer of ice  
is acceptable), this is also evidence that the temperature in the  
evaporator is too low ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
– Empty the refrigerant circuit, renew all reservoirs/receivers  
with dryer or desiccant cartridge and then evacuate the refrig‐  
erant circuit for at least 3 hours ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual) and  
⇒ “2 Working with air conditioner service station”, page 129 .  
Conditions for testing  
♦ Observe the general information on checking pressures in the  
refrigerant circuit  
⇒ “2.14.1 General information on checking pressures in the  
refrigerant circuit”, page 170  
2. Working with air conditioner service station  
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Note  
All of the conditions for testing marked with * are pertinent to a  
certain vehicle and are described in the vehicle-specific workshop  
manual ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific workshop man‐  
ual).  
General conditions for testing (these only have an influence on  
the display of the pressure gauges during this measurement with  
the air conditioning system switched on)  
•
•
Radiator and condenser are clean (clean them if necessary).*  
The heat insulation on the expansion valve is OK and properly  
installed.*  
•
•
The poly V-belt is OK and properly tensioned. The belts for air  
conditioner compressor and alternator are in good condition  
and correctly tensioned.*  
The drive unit for the air conditioner compressor is OK and  
properly installed.*  
•
•
All air ducts, covers and seals are OK and properly installed.*  
Diagnosis of the air conditioning system finds no faults (with  
the engine running and the air conditioning system switched  
on), no compressor deactivation conditions are shown in the  
measured values (only on vehicles with diagnosis “air condi‐  
tioning system”).* ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode of air conditioning system.  
•
•
The air flow rate through the dust and pollen filter is not im‐  
paired by dirt.*  
All dash panel air vents are open.*  
lk  
Note  
♦ Depending on the engine, the air conditioner compressor is  
driven by different components (belts or drive shaft). To pro‐  
tect these components and the engine, the pulley or the air  
conditioner compressor drive unit is fitted with an overload  
protection which is tripped if the air conditioner compressor is  
not operating smoothly ⇒ Heating, air conditioning; Rep. gr.  
00 ; Repair instructions; Checking cooling output (vehicle-spe‐  
cific workshop manual) and ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Air conditioner compressor (vehicle-specific workshop  
manual).  
♦ On certain versions, the radiator fan cuts in only after the pres‐  
sure in the refrigerant circuit has exceeded a pre-set value  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system.  
Other conditions for testing (these have an influence on the dis‐  
play of the pressure gauge with this measurement)  
•
The vehicle is not exposed to the sun's rays ⇒ Heating, air  
conditioning; Rep. gr. 00 ; Repair instructions; Checking cool‐  
ing output (vehicle-specific workshop manual).  
•
•
•
Ambient temperature is above 15°C.  
The ignition is switched off.  
The air conditioner service station is connected to the refrig‐  
erant circuit  
178  
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⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
♦ ⇒ “2.14.4 Checking pressures with air conditioning system  
switched on - vehicles with mechanical air conditioning com‐  
pressor”, page 183 .  
lk  
♦ ⇒ “2.14.5 Checking pressures with air conditioning system  
switched on - vehicles with electrical air conditioning com‐  
pressor”, page 205  
Checking pressures with the ignition switched off  
Note  
♦ The switching pressures for actuation of the air conditioner  
compressor regulating valve - N280- , the air conditioning sys‐  
tem magnetic clutch - N25- (if fitted) and the radiator fan (e.g.  
radiator fan - V7- / radiator fan 2 - V177- ) are vehicle-specific  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ Once the planned measures are complete, separate the air  
conditioner service station from the refrigerant circuit and  
switch it off  
⇒ “2.8 Switching off air conditioner service station and sepa‐  
rating from refrigerant circuit”, page 151 .  
•
The engine is at operating temperature (at an ambient tem‐  
perature less than 25°C).  
Note  
♦ Should the engine not be at operating temperature, take the  
vehicle for a short drive.  
♦ To test the cooling output, the engine does not have to be at  
operating temperature. However, to demand a certain cooling  
output from the air conditioning system at an ambient temper‐  
ature of less than 25°C, the engine is required to be warm if  
ambient temperatures are low.  
♦ Observe the test prerequisites ⇒ page 176 .  
– On vehicles with high-voltage system, switch off “stationary air  
conditioning” function (deactivate)⇒ Owner's Manual and ⇒  
Operating instructions of infotainment / MMI .  
– Switch off ignition.  
– Connect the air conditioner service station  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
– Check the pressures in the refrigerant circuit with the engine  
stationary.  
– Take pressure readings from pressure gauges of air condi‐  
tioner service station . Two results may be displayed:  
♦ The pressure in the refrigerant circuit is lower than indicated  
in the following table ⇒ page 182 .  
♦ The pressure in the refrigerant circuit is equal to or greater than  
that in the following table ⇒ page 183 .  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ Vapour pressure table for R1234yf refrigerant  
⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17  
♦ On vehicles with high-voltage system and auxiliary air condi‐  
tioning system functions (“heat pump mode” or “cooling of  
high-voltage battery”), valves may be installed in the refriger‐  
ant circuit that are not open when de-energised. These valves  
are opened and closed e.g. via incremental motors and are no  
longer actuated when the ignition is switched off. Depending  
lk  
on the last operating status of the air conditioning system, cer‐  
tain areas of the refrigerant circuit could be isolated by these  
valves. Depending on the layout of the service connections in  
the refrigerant circuit, these could be in an area that is isolated  
(e.g. the area with the service connection on the high pressure  
side). If necessary, these valves must be opened before the  
pressure is tested ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual) and  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode.  
♦ The pressures given in the table are slightly lower than speci‐  
fied in the vapour pressure table for the R1234yf refrigerant.  
The evaporation pressure of the refrigerant in the refrigerant  
circuit is orientated around the coldest component and could  
therefore also be slightly lower in a correctly charged refriger‐  
ant circuit than that specified for the R1234yf refrigerant in the  
vapour pressure table.  
Ambient temperature (in de‐ Pressure in the refrigerant cir‐  
grees C)  
+15 °C  
+20 °C  
+25 °C  
+30 °C  
+35 °C  
+40 °C  
+45 °C  
cuit in bar positive pressure  
3.5  
4.4  
5.3  
6.3  
7.4  
8.6  
10.0  
180  
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Note  
♦ The temperature of the components of the refrigerant circuit  
should be the same as the ambient temperature. If individual  
components of the refrigerant circuit are warmer or colder, the  
pressure will deviate from the values shown in the tables.  
♦ Absolute pressure means that 0 bar corresponds to an abso‐  
lute vacuum. The normal ambient pressure corresponds to 1  
bar absolute pressure. On most pressure gauges, a reading  
of 0 bar corresponds to an absolute pressure of one bar (which  
is confirmed by the existence of a -1 bar marking beneath the  
0 scale marking).  
♦ On vehicles with pressure senders ( high pressure sender -  
G65- , pressure sender for refrigerant circuit - G805- or refrig‐  
erant pressure and temperature sender - G395- , etc.) for  
which the measured pressure is displayed in the measured  
values of the diagnosis, the measured pressure should corre‐  
late with the values in the table (or be slightly higher) ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air condi‐  
tioning system and ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
workshop manual).  
lk  
♦ The pressure is given in different units, 1 MPa (megapascal)  
equates to 10 bar overpressure or 145 psi. At 0 bar overpres‐  
sure, 1 bar absolute pressure is approximately the same as  
ambient pressure (atmospheric pressure).  
If the measured values are OK and there is no complaint:  
– Unscrew (close) the handwheels of the quick-release coupling  
adapters ⇒ Operating instructions air conditioner service sta‐  
tion .  
– Extract the refrigerant from the two charge hoses using the air  
conditioner service station as instructed in the relevant oper‐  
ating manual ⇒ Operating instructions air conditioner service  
station .  
– Switch off the air conditioner service station (and isolate it from  
the power supply if necessary)  
⇒ “2.8 Switching off air conditioner service station and sepa‐  
rating from refrigerant circuit”, page 151 .  
If the measured values are OK and there is complaint:  
– Check the cooling output of the air conditioning system ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual)  
and watch the pressures in the refrigerant circuit.  
♦ ⇒ “2.14.4 Checking pressures with air conditioning system  
switched on - vehicles with mechanical air conditioning com‐  
pressor”, page 183 .  
♦ ⇒ “2.14.5 Checking pressures with air conditioning system  
switched on - vehicles with electrical air conditioning com‐  
pressor”, page 205  
If the measured values are not OK:  
– Investigate the cause of the deviation and rectify.  
2. Working with air conditioner service station  
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Note  
♦ If the pressures are too low, it could be because there is too  
little refrigerant in the circuit ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Technical data (vehicle-specific workshop manual)  
and ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
♦ If the pressures are too high, there may be too much refriger‐  
ant or refrigerant oil in the circuit. Empty the refrigerant circuit  
using the air conditioner service station  
⇒ “2.4 Emptying refrigerant circuit”, page 137 . If the extracted  
refrigerant volume is greater than the specified fill capacity for  
the R1234yf refrigerant ⇒ Heating, air conditioning; Rep. gr.  
00 ; Technical data (vehicle-specific workshop manual), evac‐  
uate the refrigerant circuit and recharge with the correct  
amount of R1234yf refrigerant. Then repeat the test. If the ex‐  
tracted quantity of refrigerant roughly equates to the specified  
fill capacity for the R1234yf refrigerant or is less, clean the re‐  
frigerant circuit with refrigerant  
lk  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then add the  
specified amount of refrigerant oil, evacuate the refrigerant  
circuit, recharge with the correct volume of R1234yf refrigerant  
and repeat the test.  
♦ If the pressures are too low or too high and contaminated re‐  
frigerant is found during the gas analysis, this may be the  
cause of the deviation (different refrigerants have varying va‐  
pour pressures). Empty the refrigerant circuit and then clean  
with R1234yf refrigerant  
⇒ “2.3 Performing gas analysis of refrigerant”, page 134 ,  
⇒ “2.4 Emptying refrigerant circuit”, page 137 and  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
The pressure in the refrigerant circuit is lower than indicated in  
the table  
Too little refrigerant in circuit.  
– Check for leaks in the refrigerant circuit  
⇒ “1.4 Investigating leaks”, page 68 .  
– Check the high pressure safety valve  
⇒ “1.2.17 High-pressure safety valve”, page 53 .  
If the high pressure safety valve has blown (check  
⇒ “1.2.17 High-pressure safety valve”, page 53 ):  
– Check radiator fan actuation or the radiator fan ⇒ Vehicle di‐  
agnostic tester in “Guided Fault Finding” mode - air condition‐  
ing system.  
– On vehicles with shut-off valves for the refrigerant circuit,  
check the actuation and function of these shut-off valves ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode - air  
conditioning system (and battery control) and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
– Check refrigerant lines and refrigerant hoses for signs of  
crushing (bottle-neck), external damage and tight bends ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual) and ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
– If no fault can be detected, clean the refrigerant circuit  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
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The pressure in the refrigerant circuit is equal to or greater than  
that in the table  
♦ ⇒ “2.14.4 Checking pressures with air conditioning system  
switched on - vehicles with mechanical air conditioning com‐  
pressor”, page 183 .  
♦ ⇒ “2.14.5 Checking pressures with air conditioning system  
switched on - vehicles with electrical air conditioning com‐  
pressor”, page 205  
2.14.4  
Checking pressures with air condition‐  
ing system switched on - vehicles with  
mechanical air conditioning compressor  
lk  
Checking pressures ⇒ page 183  
Specifications for pressures in the refrigerant circuit  
⇒ page 187  
Checking pressures  
Refrigerant circuit with expansion valve, receiver with or without  
air conditioning system magnetic clutch - N25- and air conditioner  
compressor regulating valve - N280- (with externally regulated air  
conditioner compressor)  
Note  
♦ Connect the air conditioner service station  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
♦ If on vehicles with two evaporators a problem is encountered  
in just one evaporator, check the pressures in the refrigerant  
circuit. If these are OK, check the line connection between the  
evaporator that is causing the problem and the outlet of the  
line connection at the distribution point of the refrigerant lines  
(for bottle-neck or blockage). If no fault can be determined,  
empty the refrigerant circuit and recharge with the prescribed  
amount of refrigerant. Then check the pressures and the cool‐  
ing output of the air conditioner again. If the problem persists,  
replace the expansion valve upstream of the problematic  
evaporator ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
♦ ⇒ “2.14.3 Checking pressures in the refrigerant circuit with the  
ignition switched off”, page 176  
Conditions for testing  
•
The air conditioner service station is connected to the refrig‐  
erant circuit  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
•
•
Observe the conditions for testing pressures in the refrigerant  
circuit with the ignition switched off ⇒ page 176 .  
The pressures in the refrigerant circuit comply with the speci‐  
fications with the ignition switched off  
⇒ “2.14.3 Checking pressures in the refrigerant circuit with the  
ignition switched off”, page 176 .  
•
Observe the conditions for testing the cooling output ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions; Check‐  
ing cooling output (vehicle-specific workshop manual).  
2. Working with air conditioner service station  
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Note  
♦ The switching pressures for actuation of the air conditioner  
compressor regulating valve - N280- , the air conditioning sys‐  
tem magnetic clutch - N25- (if fitted) and the radiator fan - V7-  
are vehicle-specific ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode - air conditioning system.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
•
The engine is at operating temperature (at an ambient tem‐  
perature less than 25°C).  
Note  
♦ Should the engine not be at operating temperature, take the  
vehicle for a short drive.  
♦ To test the cooling output, the engine does not have to be at  
operating temperature. However, to demand a certain cooling  
output from the air conditioning system at an ambient temper‐  
ature of less than 25°C, the engine is required to be warm if  
ambient temperatures are low.  
lk  
– Start engine.  
– Set the air conditioning system to maximum cooling output ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual).  
•
The air conditioner compressor is actually driven with the en‐  
gine running (visual check ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific workshop man‐  
ual)).  
•
The air conditioner compressor regulating valve - N280- is ac‐  
tuated ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system.  
Note  
♦ Depending on the engine, the air conditioner compressor is  
driven by different components (belts or drive shaft). To pro‐  
tect these components and the engine, the pulley or the air  
conditioner compressor drive unit is fitted with an overload  
protection which is tripped if the air conditioner compressor is  
not operating smoothly ⇒ Heating, air conditioning; Rep. gr.  
87 ; Air conditioner compressor (vehicle-specific workshop  
manual).  
♦ On vehicles with air conditioner compressor regulating valve -  
N280- , the control current can be gleaned from the measured  
values ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system.  
If the air conditioner compressor is not driven or the regulating  
valve not activated when the engine is running:  
– Determine the cause, e.g. by interrogating the event memory  
of the air conditioning system, and rectify it ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode - air conditioning  
system.  
184  
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– If fitted, check the voltage supply for the air conditioning sys‐  
tem magnetic clutch - N25- . If this is OK, repair the magnetic  
clutch ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific workshop manual).  
– Check actuation of the air conditioner compressor regulating  
valve - N280- ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
lk  
Note  
♦ On air conditioner compressors with an air conditioning sys‐  
tem magnetic clutch - N25- , the air conditioner compressor  
only works (delivers refrigerant) if in addition to the air condi‐  
tioner compressor regulating valve - N280- , -N25- is actuated  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system.  
♦ -N280- (and -N25- ) is actuated by the air conditioning system  
control unit - J301- , the operating and display unit for front air  
conditioning system - E87- and the Climatronic control unit -  
J255- or a downstream control unit ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ All of the conditions for testing marked with * are pertinent to  
a certain vehicle and are described in the vehicle-specific  
workshop manual ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions (vehicle-specific workshop manual) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
•
•
•
The radiator and condenser are clean (clean if necessary) * ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
The heat insulation on the expansion valve is OK and mounted  
correctly * ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
The poly V-belt is OK and properly tensioned. The belts for air  
conditioner compressor and alternator are in good condition  
and correctly tensioned.* ⇒ Heating, air conditioning system;  
Rep. gr. 87 ; Air conditioner compressor (vehicle-specific  
workshop manual) and ⇒ Heating, air conditioning system;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual).  
•
The drive unit for the air conditioner compressor is OK and  
mounted properly * ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Air conditioner com‐  
pressor (vehicle-specific workshop manual).  
•
•
The air ducts, covers and seals are OK and mounted correctly  
* ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting  
locations - air conditioning system (vehicle-specific workshop  
manual).  
Diagnosis of the air conditioning system finds no faults (with  
the engine running and the air conditioning system switched  
on), no compressor deactivation conditions are shown in the  
measured values of the respective control unit (only on vehi‐  
cles with diagnosis “air conditioning system”).* ⇒ Vehicle di‐  
agnostic tester in “Guided Fault Finding” mode of air  
conditioning system.  
•
The air flow rate through the dust and pollen filter is not im‐  
paired by dirt.* ⇒ Heating, air conditioning system; Rep. gr.  
2. Working with air conditioner service station  
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87 ; Overview of fitting locations - air conditioning system (ve‐  
hicle-specific workshop manual).  
•
•
The heater and air conditioner does not draw any secondary  
air at highest fresh air blower speed. The evaporator and heat‐  
er are not drawing in secondary air at the highest fresh air  
lk  
blower speed * ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Overview of fitting locations - air conditioning system (vehicle-  
specific workshop manual).  
The air flaps in the heating and air conditioning unit, in the  
heating and in the evaporator reach their end position * ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual)  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system (vehicle-specific  
workshop manual).  
•
The fresh air intake ducts under the bonnet and in the pas‐  
senger compartment and the corresponding water drain  
valves are OK * ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
workshop manual) and ⇒ Heating, air conditioning; Rep. gr.  
87 ; Overview of fitting locations - air conditioning system (ve‐  
hicle-specific workshop manual).  
•
•
Engine warm.  
The vehicle is not exposed to the sun's rays ⇒ Heating, air  
conditioning; Rep. gr. 00 ; Repair instructions; Checking cool‐  
ing output (vehicle-specific workshop manual).  
•
•
Ambient temperature is above 15°C.  
All dash panel diffusers are open * ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air duct system (vehicle-specific workshop man‐  
ual).  
Setting e.g. on operating and display unit for front air conditioning  
system - E87- and Climatronic control unit - J255- or air condi‐  
tioning system control unit - J301- (and operating and display unit  
for rear Climatronic - E265- on vehicles with two heating and air  
conditioning units) * ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
workshop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Overview of fitting locations - air conditioning system (vehicle-  
specific workshop manual).  
Setting on -E87- / -J255- *: ⇒ Heating, air conditioning; Rep. gr.  
00 ; Repair instructions; Checking cooling output (vehicle-specific  
workshop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Overview of fitting locations - air conditioning system (vehicle-  
specific workshop manual).  
– Select “Auto” mode (air conditioner compressor switched on).  
– Set temperature to “cold” or “LO” for the driver and front pas‐  
senger side (and the rear on the left and right in vehicles with  
two heating and air conditioning units).  
Setting on -J301- *:  
– Press A/C button and Rec or recirculate buttons.  
– Turn rotary temperature knob in direction of “cold” stop.  
– Set rotary fresh air blower switch to “4” (maximum fresh air  
blower speed).  
The following conditions for testing should then be met in the sys‐  
tem:  
•
The radiator fan - V7- is running or the radiator fan - V7- and  
radiator fan 2 - V177- are running (at least stage 1) * ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions; Check‐  
186  
Rep. gr.87 - Air conditioning system  
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ing cooling output (vehicle-specific workshop manual) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Overview of fitting lo‐  
cations - air conditioning system (vehicle-specific workshop  
manual).  
Note  
On certain versions, the radiator fan cuts in only after the pressure  
in the refrigerant circuit has exceeded a pre-set value ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning  
system.  
lk  
•
The fresh air blower - V2- (and the rear fresh air blower - V80-  
on vehicles with two heating and air conditioning units) is  
running at maximum speed.*  
•
The coolant shut-off valve is closed * ⇒ Heating, air condi‐  
tioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific workshop manual) and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system (vehicle-specific workshop manual).  
•
The valves of the pump-valve unit are closed and the coolant  
circulation pump is not delivering * ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system (vehicle-specific workshop manual).  
•
•
The fresh air blower - V2- (and the rear fresh air blower - V80-  
on vehicles with two heating and air conditioning units) is  
running at maximum speed.*  
The air recirculation flap/fresh air flap is in “recirculation  
mode” (within 1 minute after starting the vehicle, the air flow  
flap closes and the air recirculation flap opens).*  
•
•
The coolant shut-off valve is closed.*  
The valves for the pump-valve unit are closed and the coolant  
circulation pump is not delivering.*  
Specifications for pressures in the refrigerant circuit  
♦ Observe the conditions for testing and the pressures  
⇒ page 183 .  
Testing:  
– Raise engine speed to 2000 rpm.  
– Observe pressure display (e.g. pressure gauge) of air condi‐  
tioner service station ⇒ Operating instructions of air condi‐  
tioner service station .  
Note  
♦ The switching pressures for actuation of the air conditioner  
compressor regulating valve - N280- and the radiator fan are  
vehicle-specific ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
2. Working with air conditioner service station  
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High-pressure side:  
Rising from starting pressure (when pressure gauge is connec‐  
ted) to maximum 20 bar.  
Low-pressure side:  
From the output pressure (when connecting the pressure gauge)  
dropping to a value of between 1.5 and 2.3 bar absolute pressure  
(depending on required cooling output).  
lk  
188  
Rep. gr.87 - Air conditioning system  
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lk  
Note  
♦ In the event of a very high cooling output (e.g. at high outside  
temperatures and high fresh air blower speed while the engine  
is running slowly), the air conditioner compressor is initially  
incapable of changing the pressure on the low pressure side  
to the specified level (e.g. for a certain period after switching  
on the air conditioning system). The air conditioner compres‐  
sor is actuated with the maximum specified control current.  
However, the delivery volume of the air conditioner compres‐  
sor is not enough under these operating conditions and at this  
engine speed to lower the pressure on the low pressure side  
to the specification. One way of checking the regulating be‐  
haviour of the air conditioner compressor under these condi‐  
tions is to actuate e.g. the fresh air blower with only approx.  
40% of the maximum voltage and to check the pressures at  
reduced fresh air blower speed ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair information;  
Checking cooling output (vehicle-specific workshop manual).  
♦ If the demand on the cooling output is low (e.g. at an ambient  
temperature of 20°C and a low fresh air blower speed), pres‐  
sure on the high pressure side may only increase up to a value  
of 6 to 7 bar (the energy exchange is low, the refrigerant is  
cooled down quickly in the condenser). To check the regulat‐  
ing behaviour and the pressures in the refrigerant circuit under  
these conditions, e.g. actuate the fresh air blower with maxi‐  
mum voltage, set the air conditioning system to maximum  
heating output and activate air recirculation ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode - air conditioning  
system and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking cooling output (vehicle-specific work‐  
shop manual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high atmospheric humidity), the pressure on the high  
pressure side can increase to a maximum of 29 bar.  
♦ The specified working current for the air conditioner compres‐  
sor regulating valve - N280- is displayed as a measured value  
by the operating and display unit for front air conditioning sys‐  
tem - E87- , the air conditioning system control unit - J301- and  
the Climatronic control unit - J255- ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system.  
♦ The high pressure measured by the high pressure sender -  
G65- , the pressure sender for refrigerant circuit - G805- and  
the refrigerant pressure and temperature sender - G395- is  
displayed as a measured value by -E87- , -J301- or -J255-  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system.  
♦ The low pressure adjusts depending on the control current for  
the air conditioner compressor regulating valve - N280- and  
the control characteristic of the expansion valve within the  
performance band of the air conditioner compressor in the tol‐  
erance range ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
♦ In unfavourable conditions (very high ambient temperatures,  
high air humidity), the performance of the air conditioner com‐  
pressor may not always be enough to reach the specified  
pressure value within the given time (it could take slightly lon‐  
ger, depending on the engine speed, for the prescribed low  
pressure to be reached).  
2. Working with air conditioner service station  
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♦ If the air conditioner compressor's capacity utilisation is above  
90%, pressure on the low pressure side could be higher than  
the specified tolerance range. The air conditioner compressor  
output is no longer sufficient in the prevailing conditions (am‐  
bient temperature, air humidity, setting of the air conditioning  
system, engine speed, etc.) to change the pressure on the low  
pressure side to approx. 2 bar.  
♦ The specified working current for the air conditioner compres‐  
sor regulating valve - N280- must be higher than 0.3 A so that  
-N280- can be actuated reliably ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system.  
♦ When setting to “maximum cooling output”, the control current  
for the air conditioner compressor regulating valve - N280- is  
regulated at approx. 0.65 A (to 0.85 A). This measured value  
is vehicle-specific and is displayed in the ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode - air conditioning sys‐  
tem.  
♦ Absolute pressure means that 0 bar corresponds to an abso‐  
lute vacuum. The normal ambient pressure corresponds to 1  
bar absolute. On most pressure gauges, a reading of 0 bar  
corresponds to an absolute pressure of 1 bar (which is con‐  
firmed by the existence of a -1 bar marking beneath the 0 scale  
marking). Depending on the respective control unit version,  
pressure can be displayed as a measured value based on ab‐  
solute or relative pressure (difference between displays 1 bar)  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Repair instructions; Checking cooling output (vehicle-  
specific workshop manual).  
♦ The temperature of the air after the evaporator, the current air  
conditioner compressor speed and the pressure of the refrig‐  
erant on the high pressure side along with the specified work‐  
ing current for the air conditioner compressor regulating valve  
- N280- are displayed e.g. as a measured value by the oper‐  
ating and display unit, the Climatronic control unit - J255-  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system.  
Possible deviations from specification,  
cause and rectification  
♦ The required cooling output is not  
reached.  
⇒ page 192  
♦ High pressure remains constant or in‐  
creases only slightly (above the pressure  
measured when the engine is station‐  
ary).  
♦ Low pressure drops quickly to the spec‐  
ification or lower.  
♦ The required cooling output is not  
reached.  
⇒ page 193  
♦ The high pressure equates to the speci‐  
fication  
♦ The low pressure equates to the specifi‐  
cation or is too low  
190  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviations from specification,  
cause and rectification  
♦ The requisite cooling output is not  
reached.  
⇒ page 194  
⇒ page 195  
♦ High pressure does not increase or only  
marginally above the pressure with the  
engine stationary  
♦ The low pressure does not drop or only  
marginally  
♦ The requisite cooling output is not  
reached.  
♦ The high pressure increases beyond the  
specified value  
♦ Low pressure drops quickly to the spec‐  
ification or lower.  
♦ The requisite cooling output is reached ⇒ page 196  
initially but after a while or after an ex‐  
tended period, the cooling output is no  
longer sufficient.  
lk  
♦ The high pressure and the low pressure  
are normal to start with  
♦ After some time, the high pressure rises  
above the specification, the low pressure  
still equates to the specification or it  
drops below the specification.  
♦ The requisite cooling output is reached ⇒ page 198  
initially but after a short or extended pe‐  
riod, the required level is no longer  
reached.  
♦ The high pressure and low pressure are  
normal to start with but after a while, the  
high pressure rises above the specifica‐  
tion and the low pressure drops to the  
specification or lower.  
♦ The high pressure and low pressure are  
normal to start with. After a while, the low  
pressure drops to the specification or  
lower and the evaporator ices up.  
♦ The requisite cooling output is reached. ⇒ page 199  
♦ The high pressure equates to the speci‐  
fication  
♦ The low pressure is too low (lower than  
the specification)  
♦ The air conditioner compressor is noisy ⇒ page 201  
(especially immediately after being  
switched on),  
♦ The requisite cooling output is reached.  
♦ High pressure normal or too high  
♦ The low pressure is normal or too high  
(the specification is not always reached)  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviations from specification,  
cause and rectification  
lk  
♦ The required cooling output is not  
reached.  
⇒ page 203  
♦ The high pressure and low pressure  
equate to the specification  
Possible deviation from specification during pressure test  
♦ The required cooling output is not reached.  
♦ High pressure remains constant or increases only slightly (above the pressure measured when the engine  
is stationary).  
♦ The low pressure does not drop or only marginally  
Possible causes for deviation from specification and rectification  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check actuation of the air conditioner compressor regulating valve - N280- and repair if necessary ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning system.  
♦ Air conditioner compressor regulating valve - N280- or air conditioner compressor defective  
– Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒ page 79  
– -N280- or renew the air conditioner compressor ⇒ page 79  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir) ⇒ page 79 and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual) as well as  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
192  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ If this problem is encountered, ensure that the air conditioner  
compressor (air conditioner compressor shaft) is actually be‐  
ing driven via the pulley/drive unit ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ; Re‐  
frigerant circuit (vehicle-specific workshop manual).  
♦ If no fault can be found for this complaint, clean the refrigerant  
circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of -N280- . If the measured  
value of -G263- is faulty, the evaporator could ice up or the  
cooling output may not be reached ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system.  
♦ If, after repeating the test when the expansion valve has been  
renewed, the air conditioning system is not operating correctly,  
clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then renew the  
air conditioner compressor and desiccant insert/desiccant car‐  
tridge (or reservoir/receiver) ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ If the expansion valve is defective (always closed or not open‐  
ing wide enough), -N280- will change to maximum power and  
the low pressure will fall to the diagram value or less (the air  
conditioner compressor is drawing the refrigerant out of the  
low pressure side) ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system. However, since no  
refrigerant can flow through the expansion valve, the required  
cooling output is not reached, the high pressure may also not  
rise or only marginally since no energy exchange is taking  
place.  
lk  
Possible deviation from specification during pressure test  
♦ The required cooling output is not reached.  
♦ The high pressure equates to the specification  
♦ The low pressure equates to the specification or is too low  
Possible causes for deviation from specification and rectification  
♦ There is too little refrigerant in the refrigerant circuit.  
♦ The expansion valve is defective.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, renew the expansion  
valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual)  
Final measures  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
Note  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of -N280- . If the measured  
value of -G263- is faulty, the evaporator could ice up or the  
cooling output may not be reached ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system.  
♦ If, after repeating the test when the expansion valve has been  
renewed, the air conditioning system is not operating correctly,  
clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then renew the  
air conditioner compressor and reservoir/receiver (or desic‐  
cant cartridge) ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
♦ The requisite cooling output is not reached.  
♦ High pressure does not increase or only marginally above the pressure with the engine stationary  
♦ The low pressure does not drop or only marginally  
Possible causes for deviation from specification and rectification  
♦ The air conditioner compressor is not driven or not driven at the specified speed  
– Check the drive of the air conditioner compressor (via belts or drive unit) ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Air conditioner compressor (vehicle-specific workshop manual).  
♦ Actuation of the air conditioner compressor regulating valve - N280- (the air conditioning system magnetic  
clutch - N25- ) is defective.  
– Check actuation of the air conditioner compressor regulating valve - N280- (and the air conditioning system  
magnetic clutch - N25- ) and repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
- air conditioning system.  
♦ Air conditioner compressor regulating valve - N280- or air conditioner compressor defective  
– Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒ page 79  
– -N280- or renew the air conditioner compressor ⇒ page 79  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir) ⇒ page 79 ,  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual) and  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ Bottle-neck or blockage in refrigerant circuit (e.g. in refrigerant line between service connection on “low  
pressure side” and air conditioner compressor).  
– Touch the refrigerant circuit by hand to feel for a drop in temperature ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual). If a drop in temperature is felt on a component,  
if there is a kink or bottle-neck in the hose or pipeline, renew this component. In the event of a blockage or  
if no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver) ⇒ page 79 and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
194  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
Note  
♦ If this problem is encountered, ensure that the air conditioner  
compressor (air conditioner compressor shaft) is actually be‐  
ing driven via the pulley / drive unit (take note of overload  
safety device) ⇒ Heating, air conditioning; Rep. gr. 87 ; Re‐  
frigerant circuit (vehicle-specific workshop manual).  
♦ On certain engines, air conditioner compressors are used that  
feature in addition to -N280- an air conditioning system mag‐  
netic clutch - N25- on the belt pulley. In the event of this  
problem, make sure that -N25- is actually being actuated and  
that the air conditioner compressor (air conditioner compres‐  
sor shaft) is being driven by the pulley ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual) and ⇒ Electronic parts catalogue .  
♦ If no fault can be found for this complaint, clean the refrigerant  
circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
lk  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of -N280- . If the measured  
value of -G263- is faulty, the evaporator could ice up or the  
cooling output may not be reached ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system.  
♦ If, after repeating the test when the expansion valve has been  
renewed, the air conditioning system is not operating correctly,  
clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then renew the  
air conditioner compressor and reservoir/receiver (or desic‐  
cant cartridge) ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
♦ If the expansion valve is defective (always closed or not open‐  
ing wide enough), -N280- will change to maximum power and  
the low pressure will fall to the diagram value or less (the air  
conditioner compressor is drawing the refrigerant out of the  
low pressure side) ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system. However, since no  
refrigerant can flow through the expansion valve, the required  
cooling output is not reached, the high pressure may also not  
rise or only marginally since no energy exchange is taking  
place.  
Possible deviation from specification during pressure test  
♦ The requisite cooling output is not reached.  
♦ The high pressure increases beyond the specified value  
♦ Low pressure drops quickly to the specification or lower.  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check the actuation of -N280- and, if necessary, repair ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system.  
♦ Constriction or obstruction in refrigerant circuit  
♦ Expansion valve defective  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Touch the refrigerant circuit by hand to feel for a drop in temperature ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual). If a drop in temperature is felt on a component,  
if there is a kink or bottle-neck in the hose or pipeline, renew this component. In the event of a blockage or  
if no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver) ⇒ page 79 and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
lk  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
Note  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ If the expansion valve is defective (always closed or not open‐  
ing wide enough) the air conditioner compressor regulating  
valve - N280- will be set to maximum power and the low pres‐  
sure value will fall to the diagram value or less (the air condi‐  
tioner compressor extracts refrigerant from the low pressure  
side). Since no refrigerant can flow through the expansion  
valve, however, the cooling output is not reached and the high  
pressure may also not increase or only increase slightly owing  
to there being no energy exchange ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ If there is too much refrigerant in the refrigerant circuit, the air  
conditioner compressor must be emptied and the desiccant  
bag (desiccant cartridge) or reservoir/receiver renewed. After  
cleaning (flushing with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 the refrigerant cir‐  
cuit, pour the correct volume of refrigerant oil in the refrigerant  
circuit ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical  
data; Approved refrigerant oils and refrigerant oil fill volumes  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
♦ If the specification is not reached again when the test is re‐  
peated but no fault can be found in the refrigerant circuit, clean  
the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
196  
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Possible deviation from specification during pressure test  
♦ The requisite cooling output is reached initially but after a while or after an extended period, the cooling  
output is no longer sufficient.  
♦ The high pressure and the low pressure are normal to start with  
♦ After some time, the high pressure rises above the specification, the low pressure still equates to the  
specification or it drops below the specification.  
Possible causes for deviation from specification and rectification  
♦ Radiator, condenser contaminated or actuation of the radiator is not OK  
– Check actuation of the radiator fan and repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
– Check condenser for contamination and clean if necessary ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual) and ⇒ Engine, mechanicals; Rep. gr. 19 ; Radiator/  
radiator fan .  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check actuation of -N280- and the measured value of evaporator output temperature sender - G263- ,  
repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system.  
♦ Too much refrigerant in the refrigerant circuit  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably greater (more than 100 g) than the prescribed fill volume  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), there was  
too much refrigerant in the refrigerant circuit Refill the refrigerant circuit with the correct volume of R1234yf  
and repeat the test.  
♦ Air conditioner compressor regulating valve - N280- or air conditioner compressor defective  
– Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒ “1.5 Renewing components”, page 79  
– -N280- or renew the air conditioner compressor ⇒ “1.5 Renewing components”, page 79  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
lk  
(vehicle-specific workshop manual) and ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ Too much refrigerant oil in the refrigerant circuit  
♦ Moisture in refrigerant circuit  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), there is too  
much refrigerant oil in the refrigerant circuit  
– Clean refrigerant circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
2. Working with air conditioner service station  
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Note  
♦ If there is too much refrigerant in the refrigerant circuit, the air  
conditioner compressor must be emptied and the desiccant  
bag (desiccant cartridge) or reservoir/receiver renewed. After  
cleaning (flushing with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 the refrigerant cir‐  
cuit, pour the correct volume of refrigerant oil in the refrigerant  
circuit ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical  
data; Approved refrigerant oils and refrigerant oil fill volumes  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ A fault in the evaporator output temperature sender - G263-  
could also cause the refrigerant circuit to ice up. With this  
complaint, also observe the measured value of -G263- ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode - air  
conditioning system and ⇒ Heating, air conditioning; Rep. gr.  
87 ; Overview of fitting locations - air conditioning system (ve‐  
hicle-specific workshop manual).  
lk  
Possible deviation from specification during pressure test  
♦ The requisite cooling output is reached initially but after a short or extended period, the required level is no  
longer reached.  
♦ The high pressure and low pressure are normal to start with but after a while, the high pressure rises above  
the specification and the low pressure drops to the specification or lower.  
♦ The high pressure and low pressure are normal to start with. After a while, the low pressure drops to the  
specification or lower and the evaporator ices up.  
Possible causes for deviation from specification and rectification  
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Possible deviation from specification during pressure test  
♦ Radiator, condenser contaminated or actuation of the radiator is not OK  
– Check actuation of the radiator fan and repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
– Check condenser for contamination and clean if necessary ⇒ Heating, air conditioning; Rep. gr. 87 ;  
lk  
Refrigerant circuit (vehicle-specific workshop manual) and ⇒ Engine, mechanicals; Rep. gr. 19 ; Radiator/  
radiator fan .  
♦ Measured value of evaporator output temperature sender - G263- faulty.  
– Check measured value and installation of -G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
function - air conditioning system and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting locations  
- air conditioning system .  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check actuation of the air conditioner compressor regulating valve - N280- and repair if necessary ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning system.  
♦ Air conditioner compressor regulating valve - N280- or air conditioner compressor defective  
– Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒ “1.5 Renewing components”, page 79  
– -N280- or renew the air conditioner compressor ⇒ “1.5 Renewing components”, page 79  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 , ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Moisture in refrigerant circuit  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– Clean refrigerant circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
Note  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ A fault in the evaporator output temperature sender - G263-  
could cause the refrigerant circuit to ice up. With this com‐  
plaint, also observe the measured value of -G263- .  
♦ If there is too much moisture in the circuit, the air conditioner  
compressor must be emptied and the desiccant bag/desiccant  
cartridge (or reservoir/receiver) renewed. After cleaning  
(flushing with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 the refrigerant cir‐  
cuit, pour the correct volume of refrigerant oil in the refrigerant  
circuit ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ The requisite cooling output is reached.  
lk  
♦ The high pressure equates to the specification  
♦ The low pressure is too low (lower than the specification)  
Possible causes for deviation from specification and rectification  
♦ Measured value of evaporator output temperature sender - G263- faulty.  
– Check measured value and installation of -G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
function - air conditioning system and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting locations  
- air conditioning system (vehicle-specific workshop manual).  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Overview of fitting locations - air conditioning system (vehicle-specific workshop  
manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop man‐  
ual).  
– Check actuation of the air conditioner compressor regulating valve - N280- and repair if necessary ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning system.  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview  
of fitting locations - air conditioning system and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit .  
♦ Air conditioner compressor regulating valve - N280- or air conditioner compressor defective  
– Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and ⇒ “1.5 Renewing components”, page 79  
– -N280- or renew the air conditioner compressor ⇒ “1.5 Renewing components”, page 79  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 , ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ In the event of the following fault “High pressure normal, low  
pressure too low”, please note the following: With this fault,  
there is a chance that the evaporator could ice up even though  
the refrigerant volume in the circuit is OK.  
♦ If the fault exists in a shut-off valve that may be installed in the  
system (shut-off valve does not open), the refrigerant circuit  
needs to be cleaned (flushed with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ). With this fault,  
it is sufficient to check actuation of the shut-off valve. If this is  
OK, renew the shut-off valve.  
♦ If the fault is in the air conditioner compressor regulating valve  
- N280- (the regulating valve is not activated, but the air con‐  
ditioner compressor still runs), it is not necessary to clean the  
refrigerant circuit (flush with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ). In this case it is  
sufficient to renew the air conditioner compressor (observe  
quantity of refrigerant oil in compressor).  
♦ If the expansion valve is defective (always closed or not open‐  
ing wide enough) the air conditioner compressor regulating  
valve - N280- will be set to maximum power and the low pres‐  
sure value will fall to the diagram value or less (the air condi‐  
tioner compressor extracts refrigerant from the low pressure  
side). However, since no refrigerant can flow through the ex‐  
pansion valve, the required cooling output is not reached, the  
high pressure may also not rise or only marginally since no  
energy exchange is taking place. With this fault, it is not nec‐  
essary to clean the refrigerant circuit (flush with R1234yf re‐  
frigerant ⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
Renewing the expansion valve is sufficient.  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of the air conditioner  
compressor regulating valve - N280- . If the measured value  
lk  
of -G263- is faulty, the evaporator could ice up or the cooling  
output may not be reached ⇒ Vehicle diagnostic tester in “Gui‐  
ded Fault Finding” mode - air conditioning system.  
Possible deviation from specification during pressure test  
♦ The air conditioner compressor is noisy (especially immediately after being switched on),  
♦ The requisite cooling output is reached.  
♦ High pressure normal or too high  
♦ The low pressure is normal or too high (the specification is not always reached)  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check actuation of the air conditioner compressor regulating valve - N280- and repair if necessary ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning system.  
♦ Check function of -N280- ; if necessary remove -N280- and check for dirt ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system, ⇒ “1.5 Renewing components”, page 79 and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (workshop manual for specific vehicle).  
♦ Renew -N280- or air conditioner compressor ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Air conditioner compressor (vehicle-specific workshop manual).  
♦ If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or renew the receiver/reservoir)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 , ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Too much refrigerant or refrigerant oil in the refrigerant circuit  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably greater (more than 100 g) than the prescribed fill volume  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), there was  
too much refrigerant in the refrigerant circuit Recharge refrigerant circuit and repeat test.  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally higher than the  
prescribed fill volume (less than 100 g) ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-  
specific workshop manual), there is too much refrigerant oil in the refrigerant circuit Clean the refrigerant  
circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 , recharge with the correct  
volume of refrigerant and refrigerant oil and repeat the test.  
♦ Expansion valve defective  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ The air conditioner compressor is defective.  
– If it is not possible to find a fault on any of the components and the extracted refrigerant volume equates  
to the specifications, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . If when cleaning the refrigerant circuit no overly high volume  
of refrigerant is found, renew the air conditioner compressor ⇒ “1.5 Renewing components”, page 79 , ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions; Checking cooling output (vehicle-specific work‐  
shop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ; Air conditioner compressor (vehicle-specific  
workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
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Note  
♦ The cause for this fault could also be too much refrigerant oil  
in the refrigerant circuit. Overfilling with refrigerant oil can oc‐  
cur if the refrigerant oil level was not checked after the air  
conditioner compressor was renewed. If there is too much re‐  
frigerant oil in the refrigerant circuit, clean the refrigerant circuit  
(flush with R1234yf refrigerant).  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
♦ If the expansion valve (or a shut-off valve that may be installed  
lk  
in the system) is defective (always closed or not opening wide  
enough) the air conditioner compressor regulating valve -  
N280- will be set to maximum power and the low pressure  
value will fall to the diagram value or less (the air conditioner  
compressor extracts refrigerant from the low pressure side).  
Since no refrigerant can flow through the expansion valve,  
however, the cooling output is not reached and the high pres‐  
sure may also not increase or only increase slightly owing to  
there being no energy exchange ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
♦ The required cooling output is not reached.  
♦ The high pressure and low pressure equate to the specification  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume roughly equates to the prescribed fill volume, measured value of evapo‐  
rator output temperature sender - G263- , actuation of air conditioner compressor regulating valve - N280- ,  
function of expansion valve faulty or fault in a different component (see below).  
♦ Measured value of evaporator output temperature sender - G263- faulty.  
– Check measured value and installation of -G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
function - air conditioning system and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting locations  
- air conditioning system ⇒ Heating, air conditioning; Rep. gr. 87 ; Air conditioner compressor (vehicle-  
specific workshop manual).  
♦ Actuation of the air conditioner compressor regulating valve - N280- is defective.  
– Check the actuation of -N280- and, if necessary, repair ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system.  
♦ Expansion valve defective  
lk  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Touch the refrigerant circuit by hand to feel for a drop in temperature ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual). If a drop in temperature is felt on a component,  
if there is a kink or bottle-neck in the hose or pipeline, renew this component. In the event of a blockage or  
if no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ Too much refrigerant oil in the refrigerant circuit  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally higher than the  
prescribed fill volume (less than 100 g) ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-  
specific workshop manual), there is too much refrigerant oil in the refrigerant circuit Clean the refrigerant  
circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 , recharge with the correct  
volume of refrigerant and refrigerant oil and repeat the test.  
♦ Expansion valve defective  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat the test  
⇒ “2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air  
conditioning compressor”, page 183  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ Check the measured values of the evaporator output temper‐  
lk  
ature sender - G263- and actuation of -N280- . If the measured  
value of -G263- is faulty, the evaporator could ice up or the  
cooling output will not be reached ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting  
locations - air conditioning system (vehicle-specific workshop  
manual).  
♦ Overfilling with refrigerant oil can occur if the refrigerant oil  
level was not checked after the air conditioner compressor  
was renewed.  
♦ If the expansion valve is defective (always open) the evapo‐  
rator temperature will no longer be controlled so that only  
gaseous refrigerant exits the evaporator. It is then possible  
that under certain operating conditions, drops of liquid will be  
drawn into the air conditioner compressor, which will hen  
cause noise (because liquid is incompressible).  
♦ If there is too much refrigerant oil in the circuit, empty the air  
conditioner compressor and, if fitted, renew the reservoir/re‐  
ceiver (or desiccant cartridge) ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual). After cleaning the refrigerant circuit (flushing with  
R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 , pour the correct  
amount of refrigerant oil in the circuit ⇒ Heating, air condi‐  
tioning; Rep. gr. 00 ; Technical data (vehicle-specific work‐  
shop manual).  
2.14.5  
Checking pressures with air condition‐  
ing system switched on - vehicles with  
electrical air conditioning compressor  
Checking pressures ⇒ page 205  
Specifications for pressures in refrigerant circuit on vehicles with‐  
out heat pump ⇒ page 210  
Specifications for pressures in refrigerant circuit on vehicles with  
heat pump ⇒ page 234  
Checking pressures  
Note  
Work on the refrigerant circuit that involves the air conditioner  
service station (checking the pressures in this case) can usually  
be carried out without the need to de-energise the high-voltage  
system.  
– To minimise the number of automatic engine starts during  
testing and measuring while operational readiness is active,  
charge the vehicle batteries e.g. with battery charger 60A -  
VAS 5904- in battery back-up mode ⇒ Electrical system; Rep.  
gr. 27 ; Battery; Charging battery and ⇒ Electrical system;  
Rep. gr. 93 ; General warnings for work on the high-voltage  
system .  
– For test and measurement work that requires the vehicle's  
drive system to be active (READY) or the ignition to be switch‐  
ed on, move the selector lever to position “P”, activate the  
2. Working with air conditioner service station  
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parking brake and arrange the tools needed so that they can‐  
not come into contact with moving components of the engine  
and so that they cannot even come near to components that  
turn when the engine is running.  
Note  
♦ Also move the selector lever to position “P”, and activate the  
parking brake before performing test and measurement work  
for which the ignition must be switched on but where the ve‐  
hicle's drive system does not need to be active (READY).  
lk  
♦ Operational readiness (vehicle’s drive system) is displayed in  
the control unit in dash panel insert - J285- via the “Powerme‐  
ter” ⇒ owner's manual .  
♦ Activating and deactivating vehicle drive system ⇒ Owner's  
manual (observe display in control unit in dash panel insert -  
J285- while doing so).  
– On vehicles with high-voltage system, switch off “stationary air  
conditioning” function (deactivate)⇒ Owner's Manual and ⇒  
Operating instructions of infotainment / MMI .  
– Switch off ignition.  
– Connect the air conditioner service station  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
Note  
If a problem is encountered in just one evaporator on vehicles with  
two evaporators (one evaporator in the heater and air conditioning  
unit and one evaporator on the heat exchanger for high-voltage  
battery), check the pressures in the refrigerant circuit Check the  
line connection between the evaporator that is causing the prob‐  
lem and the end of the line at the distribution point for the refrig‐  
erant lines (for a bottle-neck or blockage). If no fault can be found,  
empty the refrigerant circuit and recharge it with the prescribed  
amount of refrigerant. Then check the pressures and the cooling  
output of the air conditioning system again. If the problem per‐  
sists, check / renew the following components: If the problem is  
only encountered at the evaporator in the heating and air condi‐  
tioning unit, check the evaporator in the heating and air condi‐  
tioning unit (it is open in unactuated state and allows refrigerant  
to flow through). Renew the expansion valve on the evaporator in  
the heater and air conditioning unit if no fault can be found in the  
shut-off valve. If the problem is only encountered on the evapo‐  
rator in the heat exchanger for high-voltage battery, check actua‐  
tion of the shut-off valve on the expansion valve on the evaporator  
in the heat exchanger for high-voltage battery (it is closed in un‐  
actuated state and does not allow refrigerant to flow through) ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
Conditions for testing  
•
The air conditioner service station is connected to the refrig‐  
erant circuit  
⇒ “2.2 Connecting air conditioner service station to refrigerant  
circuit”, page 131 .  
•
•
Observe the conditions for testing pressures in the refrigerant  
circuit with the ignition switched off ⇒ page 176 .  
The pressures in the refrigerant circuit comply with the speci‐  
fications with the ignition switched off  
206  
Rep. gr.87 - Air conditioning system  
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⇒ “2.14.3 Checking pressures in the refrigerant circuit with the  
ignition switched off”, page 176 .  
•
Observe the conditions for testing thelckooling output ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions; Check‐  
ing cooling output (vehicle-specific workshop manual).  
Note  
♦ The switching pressures for actuation of the electrical air con‐  
ditioner compressor - V470- and the radiator fan - V7- are  
vehicle-specific ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system and battery regulation.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
•
The engine is at operating temperature (at an ambient tem‐  
perature less than 25°C).  
Note  
♦ Should the engine not be at operating temperature, take the  
vehicle for a short drive.  
♦ To test the cooling output, the engine does not have to be at  
operating temperature. However, to demand a certain cooling  
output from the air conditioning system at an ambient temper‐  
ature of less than 25°C, the engine is required to be warm if  
ambient temperatures are low.  
•
To minimise the number of automatic engine starts during  
testing and measuring while operational readiness is active,  
charge the vehicle batteries e.g. with battery charger 60A -  
VAS 5904- in battery back-up mode ⇒ Electrical system; Rep.  
gr. 27 ; Battery; Charging battery and ⇒ Electrical system;  
Rep. gr. 93 ; General warnings for work on the high-voltage  
system .  
– Activate operational readiness (engine must not run) ⇒ own‐  
er's manual .  
– Set the air conditioning system to maximum cooling output ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual).  
•
The electrical air conditioner compressor - V470- is actuated  
and runs ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system and battery regulation as well  
as ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
2. Working with air conditioner service station  
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lk  
Note  
♦ Actuation of the electrical air conditioning compressor is initi‐  
ated by the vehicle electronics. The engine speed has no  
influence on the cooling output of the air conditioning system.  
♦ The air conditioner compressor is currently not activated at the  
maximum specified speed (of approx. 8500 rpm) when the  
vehicle is stationary or driving slowly (up to a vehicle speed of  
45 km/h). The air conditioner compressor speed is restricted  
to approx. 5000 rpm.  
♦ Actuation of the electrical air conditioning compressor can be  
monitored by guided fault finding ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
battery regulation.  
♦ All of the conditions for testing marked with * are pertinent to  
a certain vehicle and are described in the vehicle-specific  
workshop manual ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
workshop manual).  
If the air conditioner compressor is not actuated with operational  
readiness active:  
– Determine the cause, e.g. by interrogating the event memory  
of the air conditioning system, and rectify it ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode - air conditioning  
system and battery regulation.  
•
The radiator and condenser are clean (clean if necessary) * ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual) and ⇒ Engine, mechanicals;  
Rep. gr. 19 ; Radiator/radiator fan .  
•
•
The heat insulation on the expansion valve is OK and mounted  
correctly * ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
The air ducts, covers and seals are OK and mounted correctly  
* ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting  
locations - air conditioning system (vehicle-specific workshop  
manual).  
•
•
No faults are found during diagnosis of the air conditioning  
system (with operational readiness (vehicle’s drive system)  
active and the air conditioning system switched on). No com‐  
pressor deactivation condition is shown in the measured valve  
block ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system and battery regulation.  
The various pressure/temperature senders and temperature  
sensors on or in the refrigerant circuit supply plausible values  
during operation of the air conditioning system, check ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Overview of fitting lo‐  
cations - air conditioning system . If no fault can be found,  
extract the refrigerant.  
•
•
The rate of air flow through the dust and pollen filter is not  
impaired by dirt * ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Overview of fitting locations - air conditioning system (vehicle-  
specific workshop manual).  
The heater and air conditioner does not draw any secondary  
air at highest fresh air blower speed. evaporator and heater  
not drawing in secondary air at maximum fresh-air blower  
speed * ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair in‐  
structions; Checking cooling output (vehicle-specific work‐  
shop manual).  
208  
Rep. gr.87 - Air conditioning system  
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•
•
The air duct flaps in the heater and air conditioner unit, heater  
and evaporator reach their end position * ⇒ Heating, air con‐  
ditioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific workshop manual).  
Fresh-air intake ducts beneath bonnet and in passenger com‐  
partment as well as corresponding water drain valves OK* ⇒  
Heating, air conditioning; Rep. gr. 87 ; Overview of fitting lo‐  
cations - air conditioning system (vehicle-specific workshop  
manual).  
•
The vehicle is not exposed to the sun's rays ⇒ Heating, air  
conditioning; Rep. gr. 00 ; Repair instructions; Checking cool‐  
ing output (vehicle-specific workshop manual).  
•
•
Ambient temperature is above 15°C.  
All dash panel air vents are open.*  
Setting e.g. on operating and display unit for front air conditioning  
system - E87- (and operating and display unit for rear air condi‐  
tioning system - E265- on vehicles with two heater and air con‐  
ditioning units) * ⇒ Heating, air conditioning system; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
workshop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Overview of fitting locations - air conditioning system .  
Setting e.g. on -E87- *:  
– Select “Auto” mode (air conditioner compressor switched on).  
– Set temperature to “cold” or “LO” for the driver and front pas‐  
senger side (and the rear on the left and right in vehicles with  
two heating and air conditioning units).*  
Setting on -J301- *:  
– Press A/C button and Rec or recirculate buttons.*  
lk  
– Turn rotary temperature knob in direction of “cold” stop.*  
– Set rotary fresh air blower switch to “4” (maximum fresh air  
blower speed).*  
The following conditions for testing should then be met in the sys‐  
tem:  
•
The radiator fan - V7- is running or the radiator fan - V7- and  
radiator fan 2 - V177- are running (at least stage 1) * ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions; Check‐  
ing cooling output (vehicle-specific workshop manual) and ⇒  
Engine, mechanicals; Rep. gr. 19 ; Radiator/radiator fan .  
Note  
On certain versions, the radiator fan cuts in only after the pressure  
in the refrigerant circuit has exceeded a pre-set value ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning  
system and battery regulation.  
•
•
•
The fresh air blower - V2- (and the rear fresh air blower - V80-  
on vehicles with two heating and air conditioning units) is  
running at maximum speed.*  
The air recirculation flap/fresh air flap is in “recirculation  
mode” (within 1 minute after starting the vehicle, the air flow  
flap closes and the air recirculation flap opens).*  
The coolant shut-off valve is closed * ⇒ Heating, air condi‐  
tioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific workshop manual) and ⇒ Heating, air  
2. Working with air conditioner service station  
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conditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system (vehicle-specific workshop manual).  
•
The valves of the pump-valve unit are closed and the coolant  
circulation pump is not delivering * ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system (vehicle-specific workshop manual).  
Note  
♦ Actuation of the electrical air conditioning compressor is initi‐  
ated by the vehicle electronics. The engine speed has no  
influence on the cooling output of the air conditioning system  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and battery regulation.  
♦ The air conditioner compressor is currently not activated at the  
maximum specified speed (of approx. 8500 rpm) when the  
vehicle is stationary or driving slowly (up to a vehicle speed of  
45 km/h). The air conditioner compressor speed is restricted  
to approx. 5000 rpm.  
♦ Actuation of the electrical air conditioning compressor can be  
monitored by guided fault finding ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
battery regulation.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Specifications for pressures in the refrigerant circuit  
♦ Specifications for pressures in refrigerant circuit on vehicles  
without heat pump ⇒ page 210  
lk  
♦ Specifications for pressures in refrigerant circuit on vehicles  
with heat pump ⇒ page 234  
Note  
♦ The specified and actual speeds for actuation of the electrical  
air conditioner compressor - V470- and the radiator fan - V7-  
are vehicle-specific ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode - air conditioning system and battery reg‐  
ulation.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Specifications for pressures in refrigerant circuit on vehicles with‐  
out heat pump  
♦ Observe the test prerequisites ⇒ page 205 .  
– Watch the pressure display (e.g. pressure gauge) of the air  
conditioner service station .  
210  
Rep. gr.87 - Air conditioning system  
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Note  
♦ The switching pressures for actuation of the electrical air con‐  
ditioner compressor - V470- and the radiator fan -V7- / -V177-  
are vehicle-specific ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode - air conditioning system and battery reg‐  
ulation.  
♦ The pressures must be measured at the service connections;  
the fitting locations of these connections are vehicle-specific  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
High-pressure side:  
From the output pressure (when the pressure gauge is connec‐  
ted) rising up to a maximum overpressure of 20 bar (depending  
on the ambient temperature and operating conditions of the air  
conditioning system).  
Low-pressure side:  
From the output pressure (when connecting the pressure gauge)  
dropping to a value of between 1.5 and 2.3 bar absolute pressure  
(depending on required cooling output).  
Speed of air conditioner compressor:  
lk  
Between 800 and 8500 rpm depending on the required cooling  
output (currently maximum 5000 rpm with vehicle stationary).  
2. Working with air conditioner service station  
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Note  
♦ The temperature of the air after the evaporator, the current air  
conditioner compressor speed and the pressure of the refrig‐  
erant on the high-pressure side are displayed as a measured  
value from various control units depending on the vehicle (e.g.  
operating and display unit, -E87- , -J255- , thermal manage‐  
ment control unit - J1024- and air conditioning system control  
unit - J301- ) ⇒ Vehicle diagnostic tester in “Guided Fault Find‐  
ing” mode - air conditioner compressor and battery regulation.  
♦ In the event of a very high cooling output (e.g. at high outside  
temperatures and high fresh air blower speed), the air condi‐  
tioner compressor is initially incapable of changing the pres‐  
sure on the low pressure side to the required level (e.g. for a  
certain period after switching on the air conditioning system).  
The air conditioner compressor is not activated with the max.  
specified (of approx. 8500 rpm), if the vehicle stands still or  
drives slowly (up to a vehicle speed of 45 km/h). The air con‐  
ditioner compressor speed is then limited to 5000 rpm. The  
maximum permissible air conditioner compressor speed limit  
is not lifted until a vehicle speed greater than approx. 45 km/  
h is reached. The output (delivery rate) of the air conditioner  
compressor at an air conditioner compressor speed of  
5000 rpm, a high ambient temperature and high fresh air blow‐  
er speed (unfavourable ambient conditions) is initially no lon‐  
ger sufficient to bring the pressure on the low pressure side  
down to the specified value. To check the regulating behaviour  
of the air conditioner compressor under these conditions, e.g.  
only actuate the fresh air blower with approx. 40% of the max‐  
imum voltage and check the pressures at reduced fresh air  
blower speed ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system and battery regulation  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
lk  
tions; Checking cooling output (vehicle-specific workshop  
manual).  
♦ If the demand on the cooling output is low (e.g. at an ambient  
temperature of 20°C and a low fresh air blower speed), pres‐  
sure on the high pressure side may only increase up to a value  
of 6 to 7 bar (the energy exchange is low, the refrigerant is  
cooled down quickly in the condenser). To check the regulat‐  
ing behaviour and the pressures in the refrigerant circuit under  
these conditions, e.g. actuate the fresh air blower with maxi‐  
mum voltage, set the air conditioning system to maximum  
heating output and activate air recirculation ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode - air conditioning  
system and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking cooling output (vehicle-specific work‐  
shop manual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high atmospheric humidity), the pressure on the high  
pressure side can increase to a maximum of 29 bar.  
♦ The specified speed of the air conditioner compressor is dis‐  
played by various control units depending on the vehicle (e.g.  
operating and display unit, -E87- , -J255- and air conditioning  
system control unit - J301- ⇒ Vehicle diagnostic tester) in  
“Guided Fault Finding” mode - air conditioning system.  
♦ The high-pressure measured by various senders (e.g. high-  
pressure sender - G65- , pressure sender for refrigerant circuit  
- G805- or refrigerant pressure and temperature sender -  
G395- ) is displayed as a measured value depending on the  
vehicle (e.g. by -E87- , -J301- , thermal management control  
unit - J1024- or -J255- ) ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode - air conditioner compressor.  
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Rep. gr.87 - Air conditioning system  
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♦ The low pressure adjusts itself depending on the speed of the  
air conditioner compressor and the regulating characteristic of  
the expansion valve within the performance band of the air  
conditioner compressor in the tolerance range (1.5 to 2.3 over‐  
pressure).  
♦ For this test, the specified speed of the air conditioner com‐  
pressor must be greater than 1500 rpm ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode - air conditioning sys‐  
tem.  
♦ For the “maximum cooling output” setting, the specified speed  
of the air conditioner compressor is regulated at approx. 4000  
to 5000 rpm. This value is vehicle-specific and is displayed as  
a measured value by the respective control unit (e.g. operating  
and display unit, -E87- , -J255- or thermal management control  
unit - J1024- ⇒ Vehicle diagnostic tester) in “Guided Fault  
Finding” mode - air conditioning system and battery regulation.  
♦ Absolute pressure means that 0 bar corresponds to an abso‐  
lute vacuum. The normal ambient pressure corresponds to 1  
bar absolute. On the scales of most pressure gauges, 0 bar  
corresponds to an absolute pressure of 1 bar (can be seen  
from -1 bar mark below 0) ⇒ Vehicle diagnostic tester in “Gui‐  
ded Fault Finding” mode - air conditioning system.  
♦ If, on a vehicle with 2 evaporators (one in the heater and air  
conditioner unit and one for battery cooling), the temperature  
lk  
measured at one evaporator meets the specification or falls  
below the specification, while on the other evaporator, how‐  
ever, the requisite specification is not reached, regulation  
works as follows: the respective control unit (e.g. battery reg‐  
ulation control unit or thermal management control unit )  
makes the electrical air conditioner compressor run at a higher  
speed via additional controls units (e.g. power and control  
electronics for electric drive and control unit for air conditioning  
compressor ) (which results in the cooling output of the air  
conditioning system rising and pressure on the low pressure  
side falling along with the evaporator temperature). If the spec‐  
ification then falls below the minimum level at one evaporator,  
the respective control unit (e.g. battery regulation control unit )  
actuates the shut-off valves (e.g. refrigerant shut-off valve 1  
or refrigerant shut-off valve 2 ) in such a way that the evapo‐  
rator that is too cold no longer has refrigerant flowing through  
it ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
- air conditioning system and battery regulation as well as ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual)  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system (vehicle-specific  
workshop manual).  
♦ Since the output of the evaporator in the battery cooling mod‐  
ule is considerably lower than the output of the evaporator in  
the heating and air conditioning unit, the requisite specified  
temperature in the battery cooling module may still be reached  
if there is insufficient refrigerant in the circuit but the specified  
temperature in the evaporator of the heating and air condi‐  
tioning unit will no longer be reached (even though the air  
conditioner compressor is actuated at a higher speed) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific workshop manual)  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific workshop manual).  
2. Working with air conditioner service station  
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Possible deviations from specification,  
cause and rectification  
♦ The requisite cooling output in the evap‐ ⇒ page 216  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ High pressure remains constant or in‐  
creases only slightly (above the pressure  
measured when the engine is stopped).  
♦ High pressure drops quickly to the spec‐  
ification or lower.  
♦ The requisite cooling output in the evap‐ ⇒ page 218  
orator in the heating and air conditioning  
unit (and in the evaporator for battery  
cooling) is reached initially. However, af‐  
ter a while or after an extended period of  
lk  
operation, the cooling output is no longer  
adequate.  
♦ The high pressure and the low pressure  
are normal to start with  
♦ After some time, the high pressure rises  
above the specification, the low pressure  
still equates to the specification or it  
drops below the specification.  
♦ The requisite cooling output in the evap‐ ⇒ page 220  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ The high pressure equates to the speci‐  
fication  
♦ The low pressure is too low (lower than  
the specification)  
♦ The air conditioner compressor is noisy ⇒ page 222  
(especially immediately after being  
switched on),  
♦ The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit and / or in the evaporator for battery  
cooling is not reached.  
♦ High pressure normal or too high  
♦ Low pressure too high (specification is  
not reached)  
♦ The requisite cooling output in the evap‐ ⇒ page 224  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ High pressure and low pressure normal  
(equate to specification)  
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Possible deviations from specification,  
cause and rectification  
♦ The requisite cooling output in the evap‐ ⇒ page 226  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ The high pressure equates to the speci‐  
fication  
♦ The low pressure equates to the specifi‐  
cation or is too low  
♦ The requisite cooling output in the evap‐ ⇒ page 227  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
lk  
cooling module) is not reached.  
♦ The high pressure equates to the speci‐  
fication  
♦ Low pressure drops quickly to the spec‐  
ification or lower.  
♦ The requisite cooling output in the evap‐ ⇒ page 228  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ The requisite cooling output is then not  
reached at the evaporator in the heater  
and air conditioning unit (the cooling out‐  
put at the evaporator in the battery cool‐  
ing module is OK).  
♦ High pressure increases only slightly  
(above the pressure measured when the  
engine is stationary) or equates to the  
specification.  
♦ Low pressure drops (possibly quickly) to  
the specification or lower.  
♦ The requisite cooling output in the evap‐ ⇒ page 229  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ The high pressure increases beyond the  
specified value  
♦ Low pressure drops quickly to the spec‐  
ification or lower.  
♦ The requisite cooling output is then not ⇒ page 232  
reached at the evaporator for battery  
cooling (the cooling output at the evapo‐  
rator in the heater and air conditioning  
unit is OK).  
♦ High pressure equates to the specifica‐  
tion or increases only slightly (above the  
pressure measured when the engine is  
stationary).  
♦ Low pressure drops to the specification  
or lower.  
2. Working with air conditioner service station  
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Possible deviations from specification,  
cause and rectification  
♦ The requisite cooling output in the evap‐ ⇒ page 233  
lk  
orator of the heating and air conditioning  
unit (and in the evaporator for the battery  
cooling module) is not reached.  
♦ High pressure does not increase or only  
marginally above the pressure with the  
engine stationary  
♦ The low pressure does not drop or only  
marginally  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ High pressure remains constant or increases only slightly (above the pressure measured when the air  
conditioner compressor is stationary).  
♦ High pressure drops quickly to the specification or lower.  
Possible causes for deviation from specification and rectification  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves. If no fault is found, renew the expansion  
valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual)  
♦ Actuation of air conditioner compressor (and if fitted refrigerant shut-off valve 1 and refrigerant shut-off  
valve 2 ) faulty ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system and  
battery regulation, ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific workshop manual), ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting locations  
- air conditioning system (vehicle-specific workshop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Air conditioner compressor (vehicle-specific workshop manual).  
– Check actuation and the function of the air conditioner compressor (and if fitted the shut-off valves, e.g.  
refrigerant shut-off valve 1 , refrigerant shut-off valve 2 ) and repair if necessary ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation. If this is OK, extract the  
refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective and must be  
renewed ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the refrigerant shut-off valves (if fitted) is defective (closed). Check the function and renew if nec‐  
essary ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system and battery  
regulation and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit; System overview - refrigerant  
circuit  
♦ Bottle-neck or blockage in refrigerant circuit (e.g. in refrigerant line between service connection on “low  
pressure side” and air conditioner compressor) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
– If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– If a hose or pipe is kinked or crushed, renew this component ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective and must be  
renewed ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ A refrigerant shut-off valve is defective (closed). Check the function and renew ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation and ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
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Possible deviation from specification during pressure test  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
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2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ If, with this problem, no fault is found during diagnosis, check  
the refrigerant circuit for a bottle-neck or blockage (a bottle-  
neck or blockage in the refrigerant circuit can also lead to one  
of these complaints). If nothing is found here either, clean the  
refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and, if fitted, temperature sensor before  
evaporator for hybrid battery and temperature sensor after  
evaporator for hybrid battery as well as actuation of air condi‐  
tioner compressor via the respective control unit ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air condi‐  
tioning system and battery regulation.  
♦ If there is a fault in the measured value of -G263- , temperature  
sensor before evaporator for hybrid battery or temperature  
sensor after evaporator for hybrid battery (depending on the  
vehicle ⇒ Vehicle diagnostic tester in “Guided Fault Finding” -  
air conditioning system and battery regulation), problems may  
also be encountered in the cooling output or the evaporator  
could ice up.  
♦ In the event of a fault in a temperature sensor, the evaporator  
may ice up even though the correct quantity of refrigerant is  
present in the refrigerant circuit.  
♦ If, after repeating the test when the expansion valve has been  
renewed, the air conditioning system is not operating correctly,  
clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then renew the  
air conditioner compressor and desiccant cartridge (or reser‐  
voir/receiver) ⇒ Heating, air conditioning; Rep. gr. 87 ; Re‐  
frigerant circuit (vehicle-specific workshop manual).  
♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit or the shut-off valve is defective (always  
closed or does not open sufficiently), the air conditioner com‐  
pressor is actuated at the maximum output and low pressure  
drops to the specification or lower (the air conditioner com‐  
pressor draws in refrigerant from the low pressure side). Since  
no refrigerant can flow through the expansion valve, however,  
the cooling output is not reached and the high pressure may  
also not increase or only increase slightly owing to there being  
no energy exchange ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode - air conditioning system and battery reg‐  
ulation and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
♦ The evaporator in the heater and air conditioning unit has a  
considerably higher output than the evaporator for battery  
cooling. Depending on the way the drive battery - A2- is cooled  
(depending on the vehicle ⇒ Vehicle diagnostic tester in “Gui‐  
ded Fault Finding” - air conditioning system and battery regu‐  
lation), the refrigerant shut-off valve 2 on the expansion valve  
in the battery cooling module is currently only actuated from a  
certain battery temperature by the respective control unit (e.g.  
by battery regulation control unit ) so that the power consumed  
by the evaporator for battery cooling is not or barely increased  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and battery regulation as well as ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
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Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator in the heating and air conditioning unit (and in the evaporator  
for battery cooling) is reached initially. However, after a while or after an extended period of operation, the  
cooling output is no longer adequate.  
♦ The high pressure and the low pressure are normal to start with  
♦ After some time, the high pressure rises above the specification, the low pressure still equates to the  
specification or it drops below the specification.  
Possible causes for deviation from specification and rectification  
♦ Radiator, condenser contaminated or actuation of the radiator is not OK  
– Check actuation of the radiator fan and repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system.  
– Check condenser for contamination and clean if necessary ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual) and ⇒ Engine, mechanicals; Rep. gr. 19 ; Radiator/  
radiator fan .  
♦ Actuation or the function of the air conditioner compressor (or, if fitted, the refrigerant shut-off valve 1 or  
refrigerant shut-off valve 2 ) is faulty.  
♦ Moisture in refrigerant circuit  
– Check the actuation of the air conditioner compressor (and if fitted the refrigerant shut-off valve 1 and  
refrigerant shut-off valve 2 ) and check the measured value of the evaporator output temperature sender  
- G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode.  
– If actuation of the air conditioner compressor (and, if fitted, the refrigerant shut-off valve 1 and refrigerant  
shut-off valve 2 ) as well as the measured value of -G263- are OK, extract the refrigerant from the refrigerant  
circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
♦ Too much refrigerant in the refrigerant circuit  
lk  
♦ Expansion valve defective  
♦ If a shut-off valve is installed in the refrigerant circuit and it does not open correctly or at all ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Moisture in refrigerant circuit  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably greater (more than 100 g) than the prescribed fill volume  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), there was  
too much refrigerant in the refrigerant circuit Recharge refrigerant circuit and repeat test.  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally higher than the  
prescribed fill volume (less than 100 g) ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-  
specific workshop manual), there is too much refrigerant oil in the refrigerant circuit Clean the refrigerant  
circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 , recharge with the correct  
volume of refrigerant and refrigerant oil and repeat the test.  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve and desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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Note  
♦ If there is too much refrigerant oil in the circuit, empty the air  
conditioner compressor and renew the reservoir/receiver (or  
desiccant cartridge) ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual). After  
cleaning the refrigerant circuit (flushing with R1234yf refriger‐  
ant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 , pour in the  
correct amount of refrigerant oil in the refrigerant circuit ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-  
lk  
specific workshop manual).  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of the air conditioner  
compressor. If the measured value of -G263- or actuation of  
the air conditioner compressor is faulty, the evaporator could  
ice up or the cooling output will not be reached ⇒ Vehicle di‐  
agnostic tester in “Guided Fault Finding” mode - air condition‐  
ing system and battery regulation as well as ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Air conditioner compressor (vehicle-specific workshop man‐  
ual).  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ A fault in -G263- or / and, if fitted, in the refrigerant shut-off  
valve for hybrid battery can also cause the refrigerant circuit  
to ice up. With this complaint, also take note of the measured  
value of -G263- and the temperature sensor after evaporator  
for hybrid battery (on vehicles with a battery cooling module)  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and battery regulation and ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Overview of fitting locations - air  
conditioning system (vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ The high pressure equates to the specification  
♦ The low pressure is too low (lower than the specification)  
Possible causes for deviation from specification and rectification  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves. If no fault is found, renew the expansion  
valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual)  
♦ Actuation or the function of the air conditioner compressor or, if fitted, the refrigerant shut-off valve 1 /  
refrigerant shut-off valve 2 is faulty.  
– Check actuation and the function of the air conditioner compressor and, if fitted, the refrigerant shut-off  
valve 1 / refrigerant shut-off valve 2 ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air con‐  
ditioning system and battery regulation.  
– Clean refrigerant circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ The expansion valve in the heater and air conditioning unit or, if fitted, in the evaporator for battery cooling  
is defective.  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit (and for the evaporator  
for battery cooling) as well as the desiccant bag/desiccant cartridge (or reservoir/receiver).  
♦ Air conditioner compressor is defective  
– Renew air conditioner compressor ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air conditioner compressor (vehicle-specific workshop manual).  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or receiver/reservoir)  
⇒ “1.5 Renewing components”, page 79 and ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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Note  
♦ In the event of the following fault “High pressure normal, low  
pressure too low”, please note the following: With this fault,  
there is a chance that the evaporator could ice up even though  
the refrigerant volume in the circuit is OK.  
♦ If the fault exists in the air conditioner compressor (it is not  
actuated but still works), it is not necessary to clean (flush with  
R1234yf refrigerant) the refrigerant circuit  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . With this fault, it  
is sufficient to renew the air conditioner compressor (take note  
of refrigerant oil in air conditioner compressor)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Technical data (vehicle-specific  
workshop manual).  
♦ If the problem is with the air conditioner compressor (the air  
conditioner compressor is actuated at excessively high speed  
by the control unit for air conditioning compressor ), the refrig‐  
erant circuit does not have to be cleaned (by flushing with  
R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ). With this fault,  
it is sufficient to renew the air conditioner compressor (take  
note of refrigerant oil in air conditioner compressor) ⇒ Heating,  
air conditioning; Rep. gr. 00 ; Technical data (vehicllke-specific  
workshop manual) and ⇒ Heating, air conditioning; Rep. gr.  
87 ; Air conditioner compressor (vehicle-specific workshop  
manual).  
♦ If the expansion valve (or one of the two expansion valves) is  
defective (always closed or does not open sufficiently), the air  
conditioner compressor is also actuated at the maximum out‐  
put and pressure drops on the low pressure side to the spec‐  
ification or lower (the air conditioner compressor draws in  
refrigerant from the low pressure side). However, since no re‐  
frigerant can flow through the defective expansion valve, the  
required cooling output in the downstream evaporator is not  
reached, the high pressure may also not rise or only marginally  
since no energy exchange is taking place. The air conditioner  
compressor can be actuated at a higher speed, however,  
since the requisite cooling output in one evaporator is not  
reached. The same also applies if operation or actuation of the  
refrigerant shut-off valve 1 or refrigerant shut-off valve 2 is  
faulty ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system and battery regulation and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- (and, if fitted, the measured values of the  
temperature sensor before evaporator for hybrid battery and  
temperature sensor after evaporator for hybrid battery ) as well  
as actuation of the air conditioner compressor by the control  
unit for air conditioning compressor . If the measured value of  
-G263- (of the temperature sensor before evaporator for hy‐  
brid battery , the temperature sensor after evaporator for  
hybrid battery - G757- ) or actuation of the air conditioner com‐  
pressor are faulty, the evaporator can ice up or the requisite  
cooling output will not be reached ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioner compressor  
and battery regulation and ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Overview of fitting locations - air conditioning system  
(vehicle-specific workshop manual).  
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Possible deviation from specification during pressure test  
♦ The air conditioner compressor is noisy (especially immediately after being switched on),  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit and / or in the evap‐  
orator for battery cooling is not reached.  
♦ High pressure normal or too high  
♦ Low pressure too high (specification is not reached)  
Possible causes for deviation from specification and rectification  
♦ Actuation or the function of the air conditioner compressor or, if fitted, the refrigerant shut-off valve 1 /  
refrigerant shut-off valve 2 is faulty.  
♦ Too much refrigerant or refrigerant oil in the refrigerant circuit.  
– Check the actuation and function of the air conditioner compressor and, if fitted, the refrigerant shut-off  
valve 1 / refrigerant shut-off valve 2 ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air con‐  
ditioning system and battery regulation. Repair if necessary. If no fault can be found, extract the refrigerant  
from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably greater (more than 100 g) than the prescribed fill volume  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), there was  
too much refrigerant in the refrigerant circuit Recharge refrigerant circuit and repeat test.  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally higher than the  
prescribed fill volume (less than 100 g) ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-  
specific workshop manual), there is too much refrigerant oil in the refrigerant circuit Clean the refrigerant  
circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 , recharge with the correct  
volume of refrigerant and refrigerant oil and repeat the test.  
♦ Expansion valve defective  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit (and for the evaporator  
lk  
for battery cooling) as well as the desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
♦ Air conditioner compressor is defective  
– Renew air conditioner compressor ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air conditioner compressor (vehicle-specific workshop manual).  
– If dirt is found in the refrigerant circuit, clean the refrigerant circuit (flush with R1234yf refrigerant) and renew  
the expansion valve and desiccant bag/desiccant cartridge (or receiver/reservoir)  
⇒ “1.5 Renewing components”, page 79 and ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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lk  
Note  
♦ The cause for this fault could also be too much refrigerant oil  
in the refrigerant circuit. Overfilling with refrigerant oil can oc‐  
cur if e.g. the refrigerant oil level was not checked after the air  
conditioner compressor was renewed  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 00 ; Technical data (vehicle-specific  
workshop manual). If there is too much refrigerant oil in the  
refrigerant circuit, clean the refrigerant circuit (flush with  
R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit (or for the evaporator for battery cooling) is  
defective (always closed or does not open sufficiently), the air  
conditioner compressor is actuated at the maximum output  
and low pressure drops to the specification or lower (the air  
conditioner compressor draws in refrigerant from the low pres‐  
sure side). However, since no refrigerant can flow through the  
expansion valve, the required cooling output is not reached,  
the high pressure may also not rise or only marginally since  
no energy exchange is taking place. The same also applies if  
operation or actuation of the refrigerant shut-off valve 1 or re‐  
frigerant shut-off valve 2 is faulty ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
battery regulation and ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ High pressure and low pressure normal (equate to specification)  
Possible causes for deviation from specification and rectification  
224  
Rep. gr.87 - Air conditioning system  
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Possible deviation from specification during pressure test  
♦ Actuation or the function of the air conditioner compressor and, if fitted, the refrigerant shut-off valve 1 or  
refrigerant shut-off valve 2 is faulty.  
♦ Insufficient refrigerant in refrigerant circuit.  
– Check the actuation and function of the air conditioner compressor and/or, if fitted, the refrigerant shut-off  
valve 1 / refrigerant shut-off valve 2 ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air con‐  
ditioning system and battery regulation. Repair if necessary ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual). If no fault can be found, extract the refrigerant from  
the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), the expansion  
valve for the evaporator or an installed shut-off valve in the heater and air conditioning unit is defective.  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the refrigerant shut-off valves (if fitted) is defective (closed). Check the function and renew if nec‐  
essary ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system and battery  
regulation and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Too much refrigerant oil in the refrigerant circuit.  
lk  
– Clean refrigerant circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit (and for the evaporator  
for battery cooling) as well as the desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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Note  
♦ The cause for this fault could also be too much refrigerant oil  
in the refrigerant circuit. Overfilling with refrigerant oil can oc‐  
cur if e.g. the refrigerant oil level was not checked after the air  
conditioner compressor was renewed  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air  
conditioning; Rep. gr. 00 ; Technical data (vehicle-specific  
workshop manual). If there is too much refrigerant oil in the  
refrigerant circuit, clean the refrigerant circuit (flush with  
R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit (or for the evaporator for battery cooling) is  
defective (always closed or does not open sufficiently), the air  
conditioner compressor is actuated at the maximum output  
and low pressure drops to the specification or lower (the air  
conditioner compressor draws in refrigerant from the low pres‐  
sure side). However, since no refrigerant can flow through the  
expansion valve, the required cooling output is not reached,  
the high pressure may also not rise or only marginally since  
no energy exchange is taking place. The same also applies if  
operation or actuation of the refrigerant shut-off valve 1 or re‐  
frigerant shut-off valve 2 is faulty ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and  
battery regulation and ⇒ Heating, air conditioning; Rep. gr.  
lk  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ The high pressure equates to the specification  
♦ The low pressure equates to the specification or is too low  
Possible causes for deviation from specification and rectification  
226  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ Actuation of the air conditioner compressor (and/or if fitted the refrigerant shut-off valve 1 , refrigerant shut-  
off valve 2 ) is faulty ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system  
and battery regulation.  
– Check the actuation and function of the air conditioner compressor (and if fitted the refrigerant shut-off  
valve 1 , refrigerant shut-off valve 2 ) and repair if necessary ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system and battery regulation. If this is OK, extract the refrigerant from the  
refrigerant circuit.  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for the  
leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual) ⇒ Heating,  
air conditioning; Rep. gr. 00 ; Technical data . Check the function of the refrigerant shut-off valves ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ A refrigerant shut-off valve is defective (closed). Check the function and renew ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation and ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Too much refrigerant oil in the refrigerant circuit.  
– Clean refrigerant circuit (flush with R1234yf refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
lk  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit (and for the evaporator  
for battery cooling) as well as the desiccant bag/desiccant cartridge (or reservoir/receiver)  
⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 218 and  
⇒ page 226 .  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ The high pressure equates to the specification  
♦ Low pressure drops quickly to the specification or lower.  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
♦ Actuation or function of air conditioner compressor defective.  
♦ Constriction or obstruction in refrigerant circuit  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation. If no fault can be found,  
touch the refrigerant circuit by hand to feel for a temperature drop ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If a temperature drop is determined in a component. If a hose or pipe is kinked or crushed, renew this  
component ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for the  
lk  
leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), check the  
function of the expansion valve and shut-off valves ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific workshop manual).  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ A refrigerant shut-off valve is defective (closed). Check the function and renew ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation and ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 218 and  
⇒ page 226 .  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ The requisite cooling output is then not reached at the evaporator in the heater and air conditioning unit  
(the cooling output at the evaporator in the battery cooling module is OK).  
♦ High pressure increases only slightly (above the pressure measured when the air conditioner compressor  
is stationary) or equates to the specification.  
♦ Low pressure drops (possibly quickly) to the specification or lower.  
Possible causes for deviation from specification and rectification  
228  
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Possible deviation from specification during pressure test  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for the  
leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), check the  
function of the expansion valve and shut-off valves ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific workshop manual).  
♦ The expansion valve for the evaporator in the heater and air conditioning unit is defective ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the refrigerant shut-off valves is defective (closed). Check the function and renew if necessary  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning system and battery regulation  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If fitted, check the function of the installed shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
– Renew the expansion valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Bottle-neck or blockage in refrigerant circuit (e.g. in refrigerant line between service connection on “low  
pressure side” and air conditioner compressor) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
lk  
(vehicle-specific workshop manual).  
♦ Actuation of the air conditioner compressor is faulty ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode - air conditioning system and battery regulation.  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode - air conditioning system and battery regulation. If no fault can be found,  
touch the refrigerant circuit by hand to feel for a temperature drop ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If a temperature drop is determined in a component. If a hose or pipe is kinked or crushed, renew this  
component (the defective expansion valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual). If there is a blockage, clean the refrigerant circuit (flush with R1234yf  
refrigerant) ⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Renew the expansion valve for the evaporator in the heater  
and air conditioning unit (and for the evaporator for battery cooling) as well as the desiccant bag/desiccant  
cartridge (or reservoir/receiver) ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 218 .  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ The high pressure increases beyond the specified value  
♦ Low pressure drops quickly to the specification or lower.  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
Possible causes for deviation from specification and rectification  
♦ Actuation or function of air conditioner compressor defective.  
♦ Constriction or obstruction in refrigerant circuit  
♦ Expansion valve defective  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
lk  
in “Guided Fault Finding” mode - air conditioning system and battery regulation. If no fault can be found,  
touch the refrigerant circuit by hand to feel for a temperature drop ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If a temperature drop is determined in a component. If a hose or pipe is kinked or crushed, renew this  
component (the defective expansion valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual).  
– If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Renew the expansion valve for the evaporator in the heater  
and air conditioning unit (and for the evaporator for battery cooling) as well as the desiccant bag/desiccant  
cartridge (or reservoir/receiver) ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ There is too little refrigerant in the refrigerant circuit.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for the  
leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), check the  
function of the refrigerant shut-off valve ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
230  
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Note  
♦ If the function of the air conditioning system is not OK when  
the test is repeated, renew the expansion valve and desiccant  
bag/desiccant cartridge (or reservoir/receiver) and, if fitted, the  
refrigerant shut-off valve ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit or the refrigerant shut-off valve 1 is defective  
(always closed or does not open sufficiently), the air condi‐  
tioner compressor is actuated at the maximum output and low  
pressure drops to the specification or lower (the air conditioner  
compressor draws in refrigerant from the low pressure side).  
Since no refrigerant can flow through the expansion valve (the  
refrigerant shut-off valve ), however, the cooling output is not  
reached and the high pressure may also not increase or only  
increase slightly owing to there being no energy exchange  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and battery regulation and ⇒ Heating,  
lk  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific workshop manual).  
♦ If the expansion valve on the evaporator for battery cooling is  
defective (or the function or actuation of the refrigerant shut-  
off valve 2 is faulty), completely closed or does not open  
sufficiently, the air conditioner compressor is likewise actuated  
with the maximum output (the requisite temperatures in the  
battery cooling module are not reached). The pressure on the  
low pressure side only drops to the specification or lower if, at  
the same time, no cooling output is required in the heater and  
air conditioning unit (the refrigerant shut-off valve 1 is actuated  
and is closed). The air conditioner compressor extracts refrig‐  
erant on the low pressure from both evaporators. Since no  
refrigerant can flow through the expansion valve in the heater  
and air conditioning unit (the refrigerant shut-off valve 1 ),  
however, and the cooling output for battery cooling is not  
reached (there is a fault in the area of battery cooling), the  
electric air conditioning compressor is actuated at a higher  
speed. However, since no more refrigerant can flow, the pres‐  
sure on the low pressure side drops below the specified value  
and the high pressure may also not increase or only increase  
slightly due to the absence of an energy exchange ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air condi‐  
tioning and battery control ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Since the output of the evaporator for battery cooling is con‐  
siderably lower than the output of the evaporator in the heating  
and air conditioning unit, the requisite specified temperature  
for battery cooling may still be reached if there is insufficient  
refrigerant in the circuit but the specified temperature in the  
evaporator of the heating and air conditioning unit will not be  
reached (even though the air conditioner compressor is actu‐  
ated at a higher speed).  
2. Working with air conditioner service station  
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♦ If there is too much refrigerant in the refrigerant circuit, the air  
conditioner compressor must be emptied and the desiccant  
bag (desiccant cartridge) or reservoir/receiver renewed. After  
cleaning (flushing with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 the refrigerant cir‐  
cuit, pour the correct volume of refrigerant oil in the refrigerant  
circuit ⇒ Heating, air conditioning; Rep. gr. 00 ; Technical  
data; Approved refrigerant oils and refrigerant oil fill volumes  
(vehicle-specific workshop manual) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual).  
♦ Observe the additional information relating to this  
⇒ page 218 .  
Possible deviation from specification during pressure test  
♦ The requisite cooling output is then not reached at the evaporator for battery cooling (the cooling output at  
the evaporator in the heater and air conditioning unit is OK).  
♦ High pressure equates to the specificatlkion or increases only slightly (above the pressure measured when  
the engine is stationary).  
♦ Low pressure drops to the specification or lower.  
Possible causes for deviation from specification and rectification  
♦ Actuation or the function of the refrigerant shut-off valve 2 , a control motor, the blower or a temperature  
sensor in or on the battery cooling module is defective. Check and repair if necessary ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode - air conditioning system and battery regulation and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ The expansion valve for the evaporator in the battery cooling module is defective.  
– Renew the expansion valve for the evaporator for battery cooling ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
– Check the function and actuation of the components for battery cooling ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode - air conditioning system and battery regulation. Check the refrigerant lines  
if no fault can be found.  
♦ Bottle-neck or blockage in refrigerant line to or from expansion valve on evaporator for battery cooling.  
– If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Renew the expansion valve for the evaporator in the heater  
and air conditioning unit (and for the evaporator for battery cooling) as well as the desiccant bag/desiccant  
cartridge (or reservoir/receiver) ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If a hose or pipe is kinked or crushed, renew this component ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
♦ Too little refrigerant in circuit.  
♦ Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
♦ If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g) ⇒  
Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for the  
leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
♦ If the extracted refrigerant volume equates to the prescribed fill volume or is marginally lower (max. 100 g)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), check the  
refrigerant shut-off valve 1 ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning  
system and battery regulation and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
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Note  
♦ To cool the drive battery - A2- (hybrid battery), the refrigerant  
shut-off valve 1 is only actuated by e.g. the battery regulation  
control unit from a certainlbkattery temperature. If, at this point,  
air conditioning operation has not already been activated, the  
electrical air conditioner compressor - V470- is actuated via  
the control unit for air conditioning compressor - J842- e.g. by  
the battery regulation control unit . The temperature of the air  
(or refrigerant) before and after the evaporator for battery cool‐  
ing is calculated by the respective control unit (e.g. battery  
regulation control unit ). If it is found that cooling down is in‐  
sufficient, this is stored in e.g. the battery regulation control  
unit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
- air conditioning system and battery regulation.  
♦ The temperature of the air (or the coolant) and thereby the  
cooling output of the evaporator for battery cooling is deter‐  
mined by the integrated temperature sensor (it cannot cur‐  
rently be measured during operation with a thermometer) and  
can therefore only be checked by means of guided fault finding  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -  
air conditioning system and battery regulation.  
♦ Observe the additional information relating to this  
⇒ page 218 .  
Possible deviation from specification during pressure test  
♦ The requisite cooling output in the evaporator of the heating and air conditioning unit (and in the evaporator  
for the battery cooling module) is not reached.  
♦ High pressure does not increase or only marginally above the pressure with the engine stationary  
♦ The low pressure does not drop or only marginally  
Possible causes for deviation from specification and rectification  
♦ No actuation of air conditioner compressor ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode.  
♦ If fitted, refrigerant shut-off valve 1 defective (closed)  
– Check the actuation and function of the air conditioner compressor (and the refrigerant shut-off valve 1 ,  
refrigerant shut-off valve 2 ) ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode - air conditioning  
system and battery regulation. If no fault can be found, renew the expansion valve on the evaporator in the  
heating and air conditioning unit ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
♦ Bottle-neck or blockage in refrigerant circuit (e.g. in refrigerant line between service connection on “low  
pressure side” and air conditioner compressor).  
– If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Renew the expansion valve for the evaporator in the heater  
and air conditioning unit (and for the evaporator for battery cooling) as well as the desiccant bag/desiccant  
cartridge (or reservoir/receiver) ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If a hose or pipe is kinked or crushed, renew this component ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
♦ The air conditioner compressor is defective.  
– Renew air conditioner compressor ⇒ “1.5 Renewing components”, page 79 and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air conditioner compressor (vehicle-specific workshop manual).  
Final measures  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Specifications for pressures in refrigerant circuit on vehicles with  
heat pump  
Note  
♦ On vehicles with high-voltage system and heat pump, the re‐  
frigerant circuit is fitted with non-return valves and electrically  
actuated valves that regulate the flow of refrigerant in the re‐  
frigerant circuit depending on the prevailing operating status.  
These valves come in different versions ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual) and ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode.  
♦ On vehicles with “heat pump” function and/or “high-voltage  
lk  
battery cooling” function, high pressure is not always at the  
service connection on the high pressure side in all operating  
conditions of the air conditioning system. On these vehicles,  
depending on the operating status of the air conditioning sys‐  
tem, pressure in the refrigerant circuit on the high pressure  
side can only be measured via the pressure/temperature  
sender installed in the refrigerant circuit ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific work‐  
shop manual) and ⇒ Vehicle diagnostic tester “Guided Fault  
Finding” mode.  
♦ The refrigerant circuit of the air conditioning system on these  
vehicles is used not only to cool the passenger compartment  
but also to cool the hybrid battery unit (via the coolant circuit  
for the high-voltage system) and to heat the passenger com‐  
partment (at low ambient temperatures) via the heat pump  
function. To ensure that these functions are effective, various  
valves, pressure and temperature senders as well as pumps  
in the refrigerant circuit and in the coolant circuit of the high-  
voltage system must be installed correctly and be in good  
working order ⇒ Heating, air conditioning; Rep. gr. 87 ; Re‐  
frigerant circuit (vehicle-specific workshop manual), ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode and ⇒ En‐  
gine, mechanicals; Rep. gr. 19 ; Cooling system/coolant  
♦ To localise the potential cause of the malfunction, various rou‐  
tines have been stored in the basic settings of the thermal  
management control unit with which the “air conditioning cool‐  
ing”, “heat pump” and “cooling components of the high-voltage  
system” functions can be actuated ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode.  
High-pressure side:  
Rising from starting pressure (when pressure gauge is connec‐  
ted) to maximum 20 bar.  
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Note  
Depending on the location of the service connection on the high  
pressure side and on the operating status, the high pressure can  
only be measured using pressure/temperature sensors installed  
in the refrigerant circuit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
Low-pressure side:  
From the output pressure (when connecting the pressure gauge)  
dropping to a value of between 1.5 and 2.3 bar absolute pressure  
(depending on required cooling output).  
Speed of air conditioner compressor:  
Between 800 and 8500 rpm depending on the required cooling  
output (currently maximum 5000 rpm with vehicle stationary).  
2. Working with air conditioner service station  
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Note  
♦ The temperature of the air after the evaporator, the current air  
conditioner compressor speed and the pressure of the refrig‐  
erant on the high pressure side are displayed as a measured  
by different control units depending on the vehicle (e.g. by the  
thermal management control unit , the operating and display  
unit for front air conditioning system or the Climatronic control  
unit ) ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system (vehicle-specific  
workshop manual) and ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode.  
♦ In the event of a very high cooling output (e.g. at high outside  
temperatures and high fresh air blower speed), the air condi‐  
tioner compressor is initially incapable of changing the pres‐  
sure on the low pressure side to the required level (e.g. for a  
certain period after switching on the air conditioning system).  
The air conditioner compressor is not activated with the max.  
specified (of approx. 8500 rpm), if the vehicle stands still or  
drives slowly (up to a vehicle speed of 45 km/h). The air con‐  
ditioner compressor speed is then limited to 5000 rpm. The  
maximum permissible air conditioner compressor speed limit  
is not lifted until a vehicle speed greater than approx. 45 km/  
h is reached. The output (delivery rate) of the air conditioner  
compressor at an air conditioner compressor speed of  
5000 rpm, a high ambient temperature and high fresh air blow‐  
er speed (unfavourable ambient conditions) is initially no lon‐  
ger sufficient to bring the pressure on the low pressure side  
down to the specified value. To check the regulating behaviour  
of the air conditioner compressor under these conditions, e.g.  
only actuate the fresh air blower with approx. 40% of the max‐  
imum voltage and check the pressures at reduced fresh air  
blower speed ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode - air conditioning system and battery regulation  
lk  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific workshop  
manual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high atmospheric humidity), the pressure on the high  
pressure side can increase to a maximum of 29 bar.  
♦ The specified speed of the air conditioner compressor is dis‐  
played as a measured value e.g. by the thermal management  
control unit ⇒ Vehicle diagnostic tester in “Guided Fault Find‐  
ing” mode.  
♦ The pressure measured by various pressure/temperature  
senders in the refrigerant circuit (low or high pressure) de‐  
pending on the respective operating status is displayed as a  
measured value by the respective control unit ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific workshop manual).  
♦ The low pressure adjusts itself depending on the speed of the  
air conditioner compressor and the regulating characteristic of  
the expansion valve (on the evaporator of the front heating and  
air conditioning unit) within the performance band of the air  
conditioner compressor in the tolerance range (1.5 to 2.3 over‐  
pressure).  
♦ The specified speed of the air conditioner compressor must  
be greater than 1500 rpm for this test.  
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♦ For the “maximum cooling output” setting, the specified speed  
is regulated at approx. 4000 to 5000 rpm. This value is vehicle-  
specific and is displayed as a measured value by the respec‐  
tive control unit ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
♦ Absolute pressure means that 0 bar corresponds to an abso‐  
lute vacuum. The normal ambient pressure corresponds to 1  
bar absolute. On most pressure gauges, a reading of 0 bar  
corresponds to an absolute pressure of 1 bar (which can be  
identified by -1 bar under the 0 scale marking).  
♦ If on a vehicle with 2 evaporators (one in the heating and air  
conditioning unit and one for cooling the high-voltage compo‐  
nents, e.g. the heat exchanger for the high-voltage battery)  
and 2 condensers (one on the front end for the air conditioning  
system and one as a heat exchanger for the heat pump func‐  
tion), the specifications for the measured temperatures or  
pressures are met on one component but not on another (de‐  
pending on the selected function), check actuation of the  
electrically actuated valves installed in the refrigerant circuit.  
When doing this, observe the pressure distribution in the re‐  
frigerant circuit depending on the installed non-return valves  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific workshop manual).  
♦ For the air conditioning system to function correctly, it is also  
important - depending on the selected function - for sufficient  
heat to be supplied to the respective heat exchangers and  
subsequently dissipated. Also note, therefore, the inclusion of  
the heat exchangers in the respective coolant circuit of the  
engine and the high-voltage system and the function of the  
pumps and valves installed therein ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop  
manual).  
♦ Since the output of the evaporator for cooling on the high-volt‐  
age components (in the battery cooling module and in the heat  
exchanger for high-voltage battery) is lower than the output of  
the evaporator in the heating and air conditioning unit, the  
requisite specified temperature in the evaporator for cooling of  
the high-voltage components may still be reached if there is  
insufficient refrigerant in the circuit but the specified tempera‐  
ture in the evaporator of the heating and air conditioning unit  
is no longer reached (even though the air conditioner com‐  
pressor is actuated at a higher speed).  
Possible deviations from specification,  
cause and rectification  
•
High pressure remains constant or in‐ ⇒ page 239  
creases only slightly (above the pressure  
measured when the engine is stopped).  
•
•
High pressure drops quickly to the spec‐  
ification or lower.  
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit and in the evaporator for cooling the  
high-voltage components is not reached.  
•
•
•
High pressure normal  
⇒ page 242  
Low pressure equates to specification  
The required cooling output is not  
reached.  
2. Working with air conditioner service station  
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Possible deviations from specification,  
cause and rectification  
•
•
High pressure normal  
⇒ page 243  
Low pressure normal or too low (lower  
than specification)  
•
The requisite cooling output is then not  
reached at the evaporator in the heater  
and air conditioning unit (the cooling out‐  
put at the evaporator to cool the high-  
voltage components is OK).  
•
•
High pressure normal  
⇒ page 244  
Low pressure normal or too low (lower  
than specification)  
•
The requisite cooling output is then not  
reached at the evaporator to cool the  
high-voltage components (the cooling  
output at the evaporator in the heating  
lk  
and air conditioning unit is OK).  
•
High pressure does not increase or only ⇒ page 245  
marginally above the pressure with the  
engine stationary.  
•
•
The low pressure does not drop or only  
marginally.  
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit and in the evaporator for cooling the  
high-voltage components is not reached.  
•
•
•
High pressure increases above specifi‐ ⇒ page 246  
cation  
Low pressure drops quickly to the spec‐  
ification  
The requisite cooling output in the evap‐  
orator of the front heating and air condi‐  
tioning unit (and/or in the evaporator  
used to cool the high-voltage compo‐  
nents) is not reached.  
•
•
The high pressure and low pressure are ⇒ page 248  
normal to start with but after a while the  
high pressure rises above the specifica‐  
tion and the low pressure drops to the  
specification or lower.  
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit (and/or in the evaporator used to  
cool the high-voltage components) is not  
reached or no longer reached.  
•
High pressure and low pressure are nor‐ ⇒ page 249  
mal at first but after a longer drive the low  
pressure falls to below the specification  
(evaporator in heater and air condition‐  
ing unit iced up).  
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Possible deviations from specification,  
cause and rectification  
•
•
•
High pressure normal  
Low pressure too low  
⇒ page 251  
⇒ page 252  
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit (and/or in the evaporator used to  
cool the high-voltage components) is not  
reached.  
•
•
•
High pressure normal or too high  
Low pressure too high  
The air conditioner compressor is noisy  
(especially immediately after being  
switched on)  
•
The requisite cooling output in the evap‐  
orator of the front heating and air condi‐  
tioning unit (and/or in the evaporator  
used to cool the high-voltage compo‐  
nents) is not reached.  
•
•
High pressure and low pressure normal ⇒ page 254  
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit and in the evaporator for cooling the  
high-voltage components is not reached.  
lk  
or  
•
High pressure and low pressure normal  
•
The air conditioner compressor is noisy  
(especially immediately after being  
switched on)  
•
The requisite cooling output in the evap‐  
orator of the heating and air conditioning  
unit (and/or in the evaporator used to  
cool the high-voltage components) is not  
reached.  
•
•
High pressure and low pressure normal ⇒ page 255  
The requisite cooling output in the evap‐  
orator of the front heating and air condi‐  
tioning unit (and in the evaporator for  
cooling the high-voltage components) is  
not reached.  
•
The requisite cooling output is not  
reached in the heat exchanger for heat  
pump operation.  
Possible deviation from specification during pressure test  
•
High pressure remains constant or increases only slightly (above the pressure measured when the engine  
is stopped).  
•
•
High pressure drops quickly to the specification or lower.  
The requisite cooling output in the evaporator of the heating and air conditioning unit and in the evaporator  
for cooling the high-voltage components is not reached.  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Possible deviation from specification during pressure test  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Too little refrigerant in circuit.  
♦ Actuation of the air conditioner compressor or one of the valves installed in the refrigerant circuit faulty.  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system . If no fault can be found, extract the refrigerant.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves. If no fault is found, renew the expansion  
valve for the evaporator in the heater and air conditioning unit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual)  
lk  
– Depending on the result, repair the actuation or renew the defective component (air conditioner compres‐  
sor, shut-off valve, expansion valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ To localise the potential cause of the malfunction, various rou‐  
tines have been stored in the basic settings of the respective  
control unit (e.g. in the thermal management control unit ) with  
which the “air conditioning cooling”, “heat pump” and “cooling  
components of the high-voltage system” functions can be ac‐  
tuated ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific workshop manual).  
♦ If no fault is found with this complaint, first check actuation of  
the electrically actuated valves installed in the refrigerant cir‐  
cuit. If no fault can be found here, remove and check the non-  
return valves installed in the refrigerant circuit. If no fault can  
be found here either, clean the refrigerant circuit (flush with  
R1234yf refrigerant). A bottle-neck or a blockage in the refrig‐  
erant circuit can also result in one of these complaints ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual) and  
⇒ “1.6 Cleaning refrigerant circuit”, page 92  
♦ On vehicles with “heat pump” function and/or “high-voltage  
battery cooling” function, high pressure is not always at the  
lk  
service connection on the high pressure side in all operating  
conditions of the air conditioning system. On these vehicles,  
depending on the operating status of the air conditioning sys‐  
tem, pressure in the refrigerant circuit on the high pressure  
side can only be measured via the pressure/temperature  
sender installed in the refrigerant circuit ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific work‐  
shop manual) and ⇒ Vehicle diagnostic tester “Guided Fault  
Finding” mode.  
♦ Before commencing the repair work, check the measured val‐  
ues of the various pressure/temperature senders installed in  
the refrigerant circuit. If there is a fault in the measured value  
of a pressure/temperature sender, problems in the cooling  
output may also be experienced or the evaporator in the front  
heating and air conditioning unit could ice up ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
workshop manual), ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode and ⇒ Current flow diagrams, Electrical  
fault finding and Fitting locations.  
♦ When checking the various functions (heat pump or cooling of  
the high-voltage battery) take note also of the actuation and  
function of the components of the coolant circuit that are rela‐  
ted to these functions ⇒ Heating, air conditioning; Rep. gr.  
87 ; Coolant circuit (vehicle-specific workshop manual).  
♦ If, after repeating the test when the expansion valve has been  
renewed, the air conditioning system is not operating correctly,  
clean the refrigerant circuit (flush with R134a refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 . Then renew air  
conditioner compressor and receiver/desiccant cartridge.  
♦ In the event of a fault in a temperature sensor, the evaporator  
may ice up even though the correct quantity of refrigerant is  
present in the circuit.  
2. Working with air conditioner service station  
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♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit is defective (always closed or does not open  
sufficiently), the air conditioner compressor is actuated at the  
maximum output and low pressure drops to the diagram value  
or lower (the air conditioner compressor draws in refrigerant  
from the low pressure side). Since refrigerant cannot flow via  
the expansion valve, however, the cooling output is not  
reached and the high pressure may also not increase or only  
increase slightly due to the absence of energy exchange ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode - air  
conditioning system and battery regulation ⇒ Heating, air con‐  
lk  
ditioning; Rep. gr. 00 ; Repair information; Checking cooling  
output (vehicle-specific workshop manual).  
♦ The evaporator in the heater and air conditioning unit has a  
higher output than the evaporator in the battery cooling mod‐  
ule. The expansion valve in front of this evaporator (the heat  
exchanger for cooling the components of the high-voltage sys‐  
tem) is currently actuated, depending on the version, only from  
or up to a certain battery temperature to cool the drive battery /  
hybrid battery unit (hybrid battery) by the respective control  
unit so that the energy exchange through this evaporator is not  
increased or only marginally ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific workshop manual).  
♦ If there is too much refrigerant in the refrigerant circuit, the air  
conditioner compressor must also be emptied (flushed) and  
the receiver/desiccant cartridge renewed. After cleaning the  
refrigerant circuit (flushing with R134a refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 , pour in the cor‐  
rect amount of refrigerant oil in the circuit (in the air conditioner  
compressor) ⇒ Heating, air conditioning; Rep. gr. 00 ; Tech‐  
nical data (vehicle-specific workshop manual).  
Possible deviation from specification during pressure test  
•
•
•
High pressure normal  
Low pressure equates to specification  
The required cooling output is not reached.  
Possible causes for deviation from specification and rectification  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Too little refrigerant in circuit.  
♦ Shut-off valve before the expansion valve for the evaporator in the front heating and air conditioning unit  
defective.  
♦ One of the other valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Expansion valve for the evaporator in the front heating and air conditioning unit defective.  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system . If no fault can be found, extract the refrigerant.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves if no fault is found ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual)  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
lk  
tioning compressor”, page 205  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Depending on the result, repair the actuation or renew the defective component (shut-off valve/expansion  
valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
•
•
High pressure normal  
Low pressure normal or too low (lower than specification)  
The requisite cooling output is then not reached at the evaporator in the heater and air conditioning unit  
(the cooling output at the evaporator to cool the high-voltage components is OK).  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Too little refrigerant in circuit.  
♦ Actuation of air conditioner compressor is defective.  
♦ Expansion valve for the evaporator in the front heating and air conditioning unit defective.  
♦ Shut-off valve before the expansion valve for the evaporator in the front heating and air conditioning unit  
defective.  
♦ One of the other valves installed in the refrigerant circuit is defective or does not work properly.  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system . If no fault can be found, extract the refrigerant.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves if no fault is found ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual)  
lk  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Depending on the result, repair the actuation or renew the defective component (shut-off valve/expansion  
valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
•
•
High pressure normal  
Low pressure normal or too low (lower than specification)  
The requisite cooling output is then not reached at the evaporator to cool the high-voltage components (the  
cooling output at the evaporator in the heating and air conditioning unit is OK).  
Possible causes for deviation from specification and rectification  
244  
Rep. gr.87 - Air conditioning system  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the pumps or one of the valves in the coolant circuit of the high-voltage battery is defective or does  
not work properly ⇒ Heating, air conditioning; Rep. gr. 87 ; Coolant circuit (vehicle-specific workshop  
manual).  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
lk  
♦ Bottle-neck or blockage in the refrigerant line to or from the expansion valve on the evaporator used to cool  
the high-voltage components  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system .  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Check the function and actuation of the components used to cool the high-voltage components ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode - air conditioning system, air conditioner compressor and  
battery regulation  
– Depending on the result, repair the actuation or renew the defective component (shut-off valve, expansion  
valve, coolant pump, coolant shut-off valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific workshop manual) and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific workshop manual).  
– Check the lines of the refrigerant circuit. If a hose or pipe is kinked or crushed, renew this component.  
– If no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
•
•
High pressure does not increase or only marginally above the pressure with the engine stationary.  
The low pressure does not drop or only marginally.  
The requisite cooling output in the evaporator of the heating and air conditioning unit and in the evaporator  
for cooling the high-voltage components is not reached.  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
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Possible deviation from specification during pressure test  
♦ No actuation of the air conditioner compressor. The air conditioner compressor is not driven.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Bottle-neck or blockage in refrigerant circuit (e.g. in refrigerant line between service connection on “low  
pressure side” and air conditioner compressor).  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Depending on the result, repair the actuation or renew the defective component (air conditioner compres‐  
sor, shut-off valve, expansion valve) ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
– Check the lines of the refrigerant circuit. If a hose or pipe is kinked or crushed, renew this component ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Touch the refrigerant circuit by hand during operation to feel for temperature drops (bottle-neck or block‐  
age). If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
– If no fault can be found in the air conditioner compressor, renew the air conditioner compressor  
⇒ “1.5 Renewing components”, page 79  
– If no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
•
•
High pressure increases above specification  
Low pressure drops quickly to the specification  
The requisite cooling output in the evaporator of the front heating and air conditioning unit (and/or in the  
evaporator used to cool the high-voltage components) is not reached.  
Possible causes for deviation from specification and rectification  
246  
Rep. gr.87 - Air conditioning system  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ Actuation or function of air conditioner compressor defective.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Constriction or obstruction in refrigerant circuit  
♦ Expansion valve defective  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Check the lines of the refrigerant circuit. If a hose or pipe is kinked or crushed, renew this component ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Touch the refrigerant circuit by hand during operation to feel for temperature drops (bottle-neck or block‐  
age). If there is a blockage, clean the refrigerant circuit (flush with R1234yf refrigerant)  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 .  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ If the expansion valve on the evaporator in the heater and air  
conditioning unit or the previously installed shut-off valve is  
defective (always closed or does not open sufficiently), the air  
conditioner compressor is actuated at the maximum output  
and low pressure drops to the specification or lower (the air  
conditioner compressor draws in refrigerant from the low pres‐  
sure side). Since no (or too little) refrigerant can flow via the  
expansion valve, however, the cooling output is not reached  
and the high pressure may also not increase or only increase  
slightly due to the absence of energy exchange ⇒ Vehicle di‐  
agnostic tester in “Guided Fault Finding” mode - air condition‐  
ing system and battery regulation ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair information; Checking cooling output (ve‐  
hicle-specific workshop manual).  
♦ If the expansion valve in front of the evaporator used to cool  
the high-voltage components is defective (or function and ac‐  
tuation are faulty), permanently closed or does not open far  
enough, the air conditioner compressor is likewise actuated  
with maximum output (the requisite temperatures in the heat  
exchanger are not reached). The pressure on the low pressure  
side then only drops to the specification or lower if, at the same  
time, no cooling output is required in the heating and air con‐  
ditioning unit. The air conditioner compressor extracts refrig‐  
erant on the low pressure from both evaporators. Since no  
refrigerant can flow through the expansion valve in the front  
heating and air conditioning unit, however, and the cooling  
output in the evaporator used to cool the high-voltage compo‐  
nents is not reached (there is a fault in the area of the evapo‐  
rator used to cool the high-voltage components), the electrical  
air conditioning compressor is actuated with a higher speed.  
However, no refrigerant can flow, which causes pressure on  
the low pressure side to drop below the specification. High  
pressure may not rise or only marginally as no energy ex‐  
change takes place. The same applies if a valve in the refrig‐  
erant circuit is not OK, if there is a fault with integration of the  
evaporator for cooling of the high-voltage components in the  
refrigerant circuit of the high-voltage system or a pump or  
valve installed there is not OK. Here, the heat exchanger for  
high-voltage battery does actually cool down but the cooled  
coolant does not reach the high-voltage components that need  
to be cooled down ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode and ⇒ Heating, air conditioning system; Rep.  
gr. 87 ; Coolant circuit (vehicle-specific workshop manual).  
lk  
♦ Further notes regarding this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
The high pressure and low pressure are normal to start with but after a while the high pressure rises above  
the specification and the low pressure drops to the specification or lower.  
•
The requisite cooling output in the evaporator of the heating and air conditioning unit (and/or in the evap‐  
orator used to cool the high-voltage components) is not reached or no longer reached.  
Possible causes for deviation from specification and rectification  
248  
Rep. gr.87 - Air conditioning system  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Actuation and function of air conditioner compressor faulty ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ Moisture in refrigerant circuit  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system .  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
lk  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
Observe the information relating to this ⇒ page 241 .  
Possible deviation from specification during pressure test  
•
High pressure and low pressure are normal at first but after a longer drive the low pressure falls to below  
the specification (evaporator in heater and air conditioning unit iced up).  
Possible causes for deviation from specification and rectification  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Actuation and function of air conditioner compressor faulty ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Moisture in refrigerant circuit  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system .  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If no fault can be found, renew the desiccant bag/desiccant cartridge (or reservoir/receiver) and evacuate  
the refrigerant circuit for at least 3 hours.  
Final measures  
lk  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
Note  
♦ With this complaint, there is no need to clean the refrigerant  
circuit (flush with R1334yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ) as there is usu‐  
ally only a small amount of moisture in the system, which can  
be removed by a longer evacuation period.  
♦ If this complaint occurs after a longer period of operation or  
only occasionally due to moisture in the refrigerant circuit (low  
pressure falls below the specification and the evaporator ices  
up), renewing the dryer (fitted within the receiver) is sufficient.  
Refrigerant circuit is then to be evacuated for at least 3 hours.  
♦ In this case, the evaporator may ice up even though the correct  
volume of refrigerant is present in the refrigerant circuit.  
♦ A fault in the evaporator output temperature sender - G263-  
and / or a pressure/temperature sender could also cause the  
refrigerant circuit to ice up. With this complaint, therefore, also  
take note of the measured values of the various pressure/  
temperature senders in the refrigerant circuit ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating,  
air conditioning; Rep. gr. 00 ; Repair information; Checking  
cooling output (vehicle-specific workshop manual).  
♦ Further notes regarding this ⇒ page 241 .  
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Rep. gr.87 - Air conditioning system  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
lk  
Possible deviation from specification during pressure test  
•
•
•
High pressure normal  
Low pressure too low  
The requisite cooling output in the evaporator of the heating and air conditioning unit (and/or in the evap‐  
orator used to cool the high-voltage components) is not reached.  
Possible causes for deviation from specification and rectification  
♦ Too little refrigerant in circuit.  
♦ Actuation or function of the air conditioner compressor defective ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning system, renew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system . If no fault can be found, extract the refrigerant.  
– Extract refrigerant from the refrigerant circuit ⇒ “2.4 Emptying refrigerant circuit”, page 137 .  
– If the extracted refrigerant volume is considerably less than the specified fill volume (more than 100 g less)  
⇒ Heating, air conditioning; Rep. gr. 00 ; Technical data (vehicle-specific workshop manual), search for  
the leak and rectify the cause ⇒ “1.4 Investigating leaks”, page 68  
– The extracted refrigerant volume approximately equates to the prescribed fill volume, check actuation of  
the air conditioner compressor and the installed shut-off valves if no fault is found ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual)  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves installed in the refrigerant circuit by means of the  
pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– Depending on the result, repair the actuation or renew the defective component (air conditioner compres‐  
sor, shut-off valve, expansion valve, pressure/temperature sender) ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific workshop manual).  
– If no fault can be found, clean the refrigerant circuit (flush with R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Note  
♦ In the event of the following fault “High pressure normal, low  
pressure too low”, please note the following: With this fault,  
there is a chance that the evaporator in the heating and air  
conditioning unit could ice up even though the refrigerant vol‐  
ume in the circuit is OK.  
♦ If the problem is with the air conditioner compressor (the air  
conditioner compressor is actuated at excessively high speed  
by the control unit for air conditioning compressor ), the refrig‐  
erant circuit does not have to be cleaned (by flushing with  
R1234yf refrigerant  
⇒ “1.6 Cleaning refrigerant circuit”, page 92 ). With this fault,  
it is sufficient to renew the air conditioner compressor (take  
note of refrigerant oil in air conditioner compressor and re‐  
plenish as necessary).  
♦ If the expansion valve in front of the evaporator used to cool  
the high-voltage components is defective (or function and ac‐  
tuation are faulty), permanently closed or does not open far  
enough, the air conditioner compressor is likewise actuated  
with maximum output (the requisite temperatures in the heat  
exchanger are not reached). The pressure on the low pressure  
side then only drops to the specification or lower if, at the same  
time, no cooling output is required in the heating and air con‐  
ditioning unit. The air conditioner compressor extracts refrig‐  
erant on the low pressure from both evaporators. Since no  
refrigerant can flow through the expansion valve in the front  
heating and air conditioning unit, however, and the cooling  
output in the evaporator used to cool the high-voltage compo‐  
nents is not reached (there is a fault in the area of the evapo‐  
rator used to cool the high-voltage components), the electrical  
air conditioning compressor is actuated with a higher speed.  
However, no refrigerant can flow, which causes pressure on  
the low pressure side to drop below the specification. High  
pressure may not rise or only marginally as no energy ex‐  
change takes place. The same applies if a valve in the refrig‐  
erant circuit is not OK, if there is a fault with integration of the  
evaporator for cooling of the high-voltage components in the  
refrigerant circuit of the high-voltage system or a pump or  
valve installed there is not OK. Here, the heat exchanger for  
high-voltage battery does actually cool down but the cooled  
coolant does not reach the high-voltage components that need  
to be cooled down ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode and ⇒ Heating, air conditioning system; Rep.  
gr. 87 ; Coolant circuit (vehicle-specific workshop manual).  
lk  
♦ A fault in the evaporator output temperature sender - G263-  
and / or a pressure/temperature sender could also cause this  
problem. Therefore, also take note of the measured values of  
the various pressure/temperature senders in the refrigerant  
circuit ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
information; Checking cooling output (vehicle-specific work‐  
shop manual).  
♦ Further notes regarding this ⇒ page 241 .  
252  
Rep. gr.87 - Air conditioning system  
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Arteon 2018 ➤ , Atlas 2017 ➤ , CC 2012 ➤ , Caddy 2016 ➤ , Crafter 201 ...  
Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017  
Possible deviation from specification during pressure test  
•
•
•
•
High pressure normal or too high  
Low pressure too high  
The air conditioner compressor is noisy (especially immediately after being switched on)  
The requisite cooling output in the evaporator of the front heating and air conditioning unit (and/or in the  
evaporator used to cool the high-voltage components) is not reached.  
Possible causes for deviation from specification and rectification  
♦ Actuation and function of air conditioner compressor faulty ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
♦ One of the valves installed in the refrigerant circuit is defective or is not working properly ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop manual).  
♦ One of the pressure/temperature senders or temperature sensors on or in the refrigerant circuit supplies  
incorrect values ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Overview of fitting locations - air conditioning system  
♦ Too much refrigerant in circuit.  
♦ Too much refrigerant oil in circuit.  
– Check the measured values of the various pressure/temperature senders and temperature sensors during  
operation of the air conditioning systeml,krenew components with false measured values ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of  
fitting locations - air conditioning system .  
– Check the actuation and function of the air conditioner compressor and repair ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode  
– Check the function and actuation of the various valves and pressure/temperature senders installed in the  
refrigerant circuit by means of the pressure distribution in the refrigerant circuit ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific workshop manual).  
– If no fault can be found, extract the refrigerant from the refrigerant circuit.  
•
The quantity of refrigerant extracted is significantly greater than the prescribed charge quantity:  
– Recharge the refrigerant circuit and repeat the test.  
The quantity of refrigerant extracted is about equal to the prescribed charge quantity:  
•
– Check the actuation and function of the air conditioner compressor and the valves installed in the refrigerant  
circuit (shut-off valves and expansion valves) ⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode.  
– Depending on the result, repair the actuation or renew the defective component (shut-off valve, expansion  
valve or air conditioner compressor as well as receiver/dryer) ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific workshop manual).  
– If no fault can be found there may be too much refrigerant oil in the circuit. Clean the refrigerant circuit  
(flush with R1234yf refrigerant ⇒ “1.6 Cleaning refrigerant circuit”, page 92 ).  
Final measures  
– Recharge the refrigerant circuit ⇒ “2.6 Charging refrigerant circuit”, page 146  
– Repeat test  
⇒ “2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air condi‐  
tioning compressor”, page 205  
2. Working with air conditioner service station  
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253  

Related Topics

Air conditioning system

1 Refrigerant circuit
1.1 System overview - refrigerant circuit
1.1.1 System overview - refrigerant circuit with expansion valve and receiver
1.1.2 System overview - refrigerant circuit with restrictor and reservoir
1.1.3 System overview - refrigerant circuit with electrically driven air conditioner compressor
1.2 General description - components of refrigerant circuit
1.2.1 Layout and function of refrigerant circuit
1.2.2 Mechanical air conditioner compressor
1.2.3 Electrical air conditioner compressor for hybrid vehicles
1.2.4 Condenser
1.2.5 Evaporator
1.2.6 Reservoir
1.2.7 Heat exchanger for heat pump mode
1.2.8 Liquid receiver
1.2.9 Restrictor
1.2.10 Receiver
1.2.11 Expansion valve (with and without shut-off valve)
1.2.12 Refrigerant shut-off valves
1.2.13 Refrigerant line with internal heat exchanger
1.2.14 Quick release couplings of refrigerant lines
1.2.15 Seals
1.2.16 Pipes and hoses in refrigerant circuit
1.2.17 High-pressure safety valve
1.2.18 Non-return valves
1.2.19 Quick-release coupling connections in refrigerant circuit
1.2.20 Connections with valve for switches in refrigerant circuit
1.2.21 Pressure senders and switches in refrigerant circuit
1.2.22 Refrigerant pressure and temperature sender
1.2.23 Air conditioner compressor regulating valve N280
1.2.24 Refrigerant temperature sender
1.3 Possible complaints
1.3.1 Prerequisites for investigating a complaint
1.3.2 Possible complaints
1.3.3 Odours from heater and air conditioner unit
1.4 Investigating leaks
1.4.1 General information about investigating leaks in the refrigerant circuit
1.4.2 Searching for leaks in refrigerant circuits using an electronic leak detector
1.4.3 Searching for leaks with UV leak detection system
1.4.4 Detecting leaks in a vacuum test using air conditioner service station, or in a pressure test
1.4.5 Detecting leaks in a pressure test (with nitrogen or compressed air)
1.5 Renewing components
1.5.1 General information about renewing components
1.5.2 Renewing leaking or damaged components of empty refrigerant circuit
1.5.3 Renewing leaking or damaged components of charged refrigerant circuit
1.5.4 Renewing air conditioner compressor with no need to clean refrigerant circuit
1.5.5 Renewing air conditioner compressor due to leaks or internal damage
1.5.6 Renewing desiccant cartridge / receiver after cleaning refrigerant circuit
1.5.7 Renewing receiver with no need to clean refrigerant circuit
1.5.8 Renewing desiccant cartridge / desiccant bag with no need to clean refrigerant circuit
1.6 Cleaning refrigerant circuit
1.6.1 General information about cleaning refrigerant circuit
1.6.2 Preparations for cleaning refrigerant circuit (flushing with R1234yf refrigerant)
1.6.3 Refrigerant circuit cleaning procedure
1.6.4 Principle circuit diagrams for cleaning (flushing circuits) - refrigerant circuit with expansion valve and receiver
1.6.5 Principle circuit diagrams for cleaning (flushing circuits) - refrigerant circuit with restrictor and receiver
1.6.6 Principle circuit diagrams for cleaning (flushing circuits) - vehicles with high-voltage system (without auxiliary)
1.6.7 Principle circuit diagrams for cleaning (flushing circuits) - vehicles with high-voltage system (with auxiliary)
1.6.8 Adapters for setting up flushing circuits
1.6.9 General information about blowing through with compressed air or nitrogen
1.6.10 Blowing through refrigerant circuit with compressed air or nitrogen
1.7 Checking pressures with pressure gauge
1.7.1 Display on pressure gauges
1.7.2 Pressure gauges enable the following test and measurement work
2 Working with air conditioner service station
2.1 Working with air conditioner service station
2.2 Connecting air conditioner service station to refrigerant circuit
2.3 Performing gas analysis of refrigerant
2.4 Emptying refrigerant circuit
2.5 Evacuating refrigerant circuit
2.6 Charging refrigerant circuit
2.7 Bringing air conditioning system into service after charging
2.8 Switching off air conditioner service station and separating from refrigerant circuit
2.9 Charging refrigerant in reservoir
2.10 Emptying air conditioner service station
2.11 Cleaning electrical air conditioning compressor
2.12 Cleaning refrigerant circuit
2.13 Filling contaminated refrigerant in a recycling cylinder for analysis, processing or disposal
2.13.1 Filling contaminated refrigerant in a recycling cylinder using technical equipment
2.13.2 Filling undercooled contaminated refrigerant in a recycling cylinder
2.14.1 General information on checking pressures in the refrigerant circuit
2.14.2 Pressures and temperatures in refrigerant circuit
2.14.3 Checking pressures in the refrigerant circuit with the ignition switched off
2.14.4 Checking pressures with air conditioning system switched on - vehicles with mechanical air conditioning compressor
2.14.5 Checking pressures with air conditioning system switched on - vehicles with electrical air conditioning compressor
3 Testing equipment and tools
3.1 Tools and materials available from distribution centre or importer
3.2 Tools and materials available commercially
3.3 Tools that can be locally manufactured

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