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1999-2005 Audi A2 SUV Checking pressures User Manual

MY CAR USER MANUAL

Checking pressures for Your Audi A2 SUV 1999-2005

Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
8
Checking pressures  
Vehicles with high-voltage system (hybrid vehicles)  
High voltage! Danger to life!  
The voltage levels in the high-voltage system constitute a safety  
hazard. Danger of severe or fatal injuries from electric shock.  
– Persons with life-sustaining or other electronic medical devi‐  
ces in or on their body must not perform any work on the high-  
voltage system. Such medical devices include internal anal‐  
gesic pumps, implanted defibrillators, pacemakers, insulin  
pumps and hearing aids.  
– The high-voltage system must be de-energised by a suitably  
qualified person.  
Risk of injury - engine may start unexpectedly  
It is difficult to determine whether the drive system of an electric  
vehicle or hybrid vehicle is active. Moving parts can trap or draw  
in parts of the body.  
– Switch off ignition.  
– Place ignition key outside vehicle.  
Risk of damage to high-voltage wiring  
Incorrect handling may result in damage to the insulation of high-  
voltage wires or high-voltage connectors.  
– Never use high-voltage wiring or high-voltage connectors as  
a support.  
– Never prop tools against high-voltage wiring or high-voltage  
connectors.  
– Never bend or kink high-voltage wiring.  
– Pay attention to coding when connecting high-voltage con‐  
nections.  
♦ For all work on vehicles with high-voltage system, note addi‐  
tional warnings for working on such vehicles  
⇒ “1 Warning instructions when working on vehicles with high-  
voltage system”, page 1 .  
♦ If work near high-voltage system components is necessary,  
perform a visual check of the high-voltage components and  
wires to check for damage ⇒ page 2 .  
♦ If work on high-voltage system components is necessary, de-  
energise high-voltage system ⇒ Rep. gr. 93 ; De-energising  
high-voltage system or ⇒ Electrical system; Rep. gr. 93 ; De-  
energising high-voltage system .  
8. Checking pressures  
193  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
When working on the refrigerant circuit using the air conditioner  
service station (here: checking pressure), the high-voltage sys‐  
tem does not usually have to be de-energised.  
– To minimise the number of automatic engine starts when the  
vehicle's drive system is active during test and measurement  
work, charge the vehicle batteries e.g. with the battery  
charger 60A - VAS 5904- in battery standby mode ⇒ Electrical  
system; General information; Rep. gr. 27 ; Battery; Charging  
battery and ⇒ Electrical system; Rep. gr. 93 ; General warning  
instructions 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  
parking brake and take care to keep well clear of the engine  
when it is running. Set up any tools needed so that they cannot  
come into contact with moving parts.  
Note  
♦ 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 vehicle's drive  
system does not need to be active.  
♦ The status of the drive system (READY) is shown by the con‐  
trol unit in dash panel insert - J285- via the “power meter” ⇒  
Owner's Manual .  
♦ Activating and deactivating drive system ⇒ Owner's Manual  
(note display of control unit in dash panel insert - J285- ).  
Vehicles with start/stop system  
Risk of injury - engine may start unexpectedly  
The engine can start unexpectedly if the vehicle's start/stop sys‐  
tem is activated. A message in the instrument cluster indicates  
whether the start/stop system is activated.  
– To deactivate the start/stop system, switch off the ignition.  
194  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
All vehicles  
⇒ “8.1 Checking pressures in refrigerant circuit with air conditioner  
service station (with ignition switched off)”, page 195  
⇒ “8.2 Checking pressures - vehicles with restrictor and reservoir  
(with internally regulated air conditioner compressor)”,  
page 201  
⇒ “8.3 Checking pressures - vehicles with expansion valve and  
receiver (with internally regulated air conditioner compressor)”,  
page 206  
⇒ “8.4 Checking pressures - vehicles with restrictor, reservoir and  
air conditioner compressor regulating valve N280 (with externally  
regulated air conditioner compressor)”, page 212  
⇒ “8.5 Checking pressures - vehicles with expansion valve, re‐  
ceiver and air conditioner compressor regulating valve N280 (with  
externally regulated air conditioner compressor)”, page 219  
⇒ “8.6 Checking pressures - vehicles with electrically driven air  
conditioner compressor (vehicles with high-voltage system)”,  
page 230  
8.1  
Checking pressures in refrigerant circuit  
with air conditioner service station (with  
ignition switched off)  
Note  
♦ All test requirements marked with an * are vehicle-specific and  
are described in the Workshop Manual for the relevant vehicle.  
♦ Check cooling output.*  
♦ Connections with valve and service connections for measuring  
and testing ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific Workshop Manual).  
♦ Depending on the version of the air conditioner compressor,  
there may be a valve on the high-pressure side of the com‐  
pressor which prevents liquid refrigerant from flowing back into  
the compressor after the air conditioner has been switched off.  
If an air conditioner compressor with such a valve is installed  
in a vehicle with a refrigerant circuit with an expansion valve,  
it may take a relatively long time before the pressure in the  
high-pressure side drops (the expansion valve is cold and the  
pressure in the low-pressure side increases rapidly after the  
compressor is switched off; the expansion valve is closed and  
the refrigerant can only flow slowly to the low-pressure side).  
If the air conditioner compressor is switched on, the pressure  
in the low-pressure side drops, the expansion valve is opened  
and the refrigerant can flow to the low-pressure side.  
Under certain operating conditions, residual moisture in the cool‐  
ant circuit may lead to the formation of ice at the air conditioner  
compressor regulating valve. Such ice formation impedes the  
control of the air conditioner compressor. The evaporator is  
cooled down too much and ices up. An iced-up evaporator may  
cause the following problems:  
♦ The air conditioning system fails repeatedly or sporadically (no  
cooling/heating output) after extended driving; after the vehicle  
has been stopped, the air conditioner functions properly again  
(after a short wait).  
♦ Misting up of the windows (front windscreen, side windows  
and / or rear windscreen) on the inside after a long journey;  
the windows are initially not cleared even by pressing the De-  
8. Checking pressures  
195  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
frost button; the air conditioner functions properly again after  
a short delay following engine shut-off.  
Remedy:  
– In the case of vehicles as of Model Year 2001 and an air con‐  
ditioner compressor with air conditioner compressor regulat‐  
ing valve - N280- , check the measured value of the evaporator  
output temperature sender - G263- (by way of the “Reading  
measured value block” function). If the measured value of the  
sender is too low under the usage conditions outlined by the  
customer (at ambient temperatures above 0 °C, below 0 °C for  
a lengthy period although -N280- is not being activated) or too  
high (above approx. 10 °C although air conditioner is operating  
properly), The evaporator may ice up due to the incorrect  
measured value ⇒ Vehicle diagnostic tester (“self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
– On vehicles without an evaporator output temperature sender  
- G263- , use for example footwell vent temperature sender -  
G192- to check vent temperature under operating conditions  
described by customer in the following settings: "Lo tempera‐  
ture" for driver and passenger side, 4 or 5 bars for fresh air  
blower speed, air outlet to footwell and fresh-air mode. If  
measured value of sender is too low (at ambient temperature  
above 0°C, colder than 0°C for lengthy period).  
– Check refrigerant line between evaporator and reservoir (thick  
line, low-pressure side) with engine running. If this line is se‐  
verely iced up when the problem occurs (thin layer of ice is  
permissible), this also indicates that evaporator temperature  
is too low.  
– Discharge refrigerant circuit, renew reservoir or receiver with  
dryer and then evacuate refrigerant circuit for at least 3 hours.  
⇒ “8.1.1 Test requirements”, page 196  
⇒ “8.1.2 Checking pressures ”, page 198  
8.1.1  
Test requirements  
Note  
This section describes the test requirements for a vehicle with a  
mechanically driven air conditioner compressor as an example.  
These requirements differ on vehicles with high-voltage system  
(e.g. Audi A3 e-tron, Audi Q7 e-tron) or with additional air condi‐  
tioner functions (e.g. Audi Q7 e-tron). On these vehicles, note the  
corresponding information in the Workshop Manual and in Guided  
Fault Finding ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking cooling output (vehicle-specific Workshop  
Manual) and ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode.  
•
•
Radiator and condenser clean (clean if necessary)  
Thermal insulation at expansion valve OK and properly instal‐  
led*  
•
Poly V-belt OK and properly tensioned. / belts for air condi‐  
tioner compressor and alternator OK and properly tensioned.*  
•
•
All air ducts, covers and seals OK and properly installed  
No faults detected during fault-finding on electrical system and  
vacuum system* ⇒ Vehicle diagnostic tester (“self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
196  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
•
•
No fault detected during air conditioner self-diagnosis (with  
engine running and air conditioning system switched on), no  
compressor shutoff criteria displayed in measured value block  
(vehicles with “air conditioning system” self-diagnosis only).*  
⇒ Vehicle diagnostic tester (“self-diagnosis” or “Guided Fault  
Finding” function for air conditioner) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
Check whether the various pressure/temperature senders and  
temperature sensors installed in the refrigerant circuit deliver  
plausible measured values during operation of the air condi‐  
tioner ⇒ Vehicle diagnostic tester (“Guided Fault Finding”) and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Overview of fitting  
locations - air conditioner . If no fault is found, extract refriger‐  
ant.  
•
•
Air flow through dust and pollen filter not impeded by dirt*  
Air conditioning unit not drawing in secondary air at maximum  
fresh air blower speed; evaporator and heater not drawing in  
secondary air at maximum fresh air blower speed*  
•
•
Air flaps in air conditioning unit, heater and evaporator reach  
end position*  
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 ; Air ducting (vehicle-  
specific Workshop Manual).  
•
•
Engine at operating temperature  
Vehicle not exposed to sunlight ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output  
(vehicle-specific Workshop Manual)  
•
•
Ambient temperature above 15 °C  
All dash panel vents open  
– Start engine.  
Setting on the air conditioning system control unit, e.g. on the op‐  
erating and display unit for front air conditioning system - E87- or  
the Climatronic control unit - J255- (and the rear Climatronic op‐  
erating and display unit - E265- on vehicles with two air condi‐  
tioning units):  
– Select “Auto” mode (air conditioner compressor switched on).  
– Set “LO” temperature for driver and front passenger side (and  
rear left and right of passenger compartment in vehicles with  
two air conditioning units).  
Settings on heater controls:  
– Press A/C button and "Rec" or recirculated air button.  
– Turn the rotary temperature control towards the “cold” stop.  
– Set rotary fresh air blower control to “4”.  
Subsequently, the following system test requirements should be  
met:  
•
Radiator fan - V7- (and radiator fan 2 - V177- if fitted) must be  
running (at least at speed 1).*  
8. Checking pressures  
197  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
With some versions, the fan is not switched on until the pressure  
in the refrigerant circuit has exceeded a specified value.  
•
Fresh air blower - V2- (and rear fresh air blower - V80- on  
vehicles with two air conditioning units) run(s) at maximum  
speed.  
•
Air recirculation flap/fresh air flap is in “Air recirculation mode”  
position (air flow flap is closed and air recirculation flap opened  
within 1 min. after the vehicle is started).*  
•
•
Coolant shut-off valve closed.*  
Valves of pump valve unit closed and no coolant circulation  
pump delivery*  
•
Air conditioner compressor is actually driven ( air conditioning  
system magnetic clutch - N25- energised, overload protection  
(if fitted) not tripped).*  
Note  
Depending on the engine, the air conditioner compressor is driven  
by different components (belt or drive shaft). To protect these  
components and the engine, the pulley or the drive unit of the air  
conditioner compressor are fitted with an overload protection de‐  
vice, which is triggered if the air conditioner compressor is not  
operating smoothly ⇒ Heating, air conditioning; Rep. gr. 87 ; Air  
conditioner compressor (vehicle-specific Workshop Manual).  
8.1.2  
Checking pressures  
♦ Observe test requirements ⇒ page 196 .  
– On vehicles with high-voltage system, switch off (deactivate)  
auxiliary air conditioner function ⇒ Owner's Manual and ⇒  
Infotainment/MMI Operating Manual .  
– Switch off ignition.  
– Connect air conditioner service station ⇒ page 187 .  
Vehicles with electrically operated valves in the refrigerant circuit  
which are not open when the system is de-energised (e.g. on the  
Audi Q7 e-tron):  
Note  
On vehicles with high-voltage system and additional air condi‐  
tioner functions (“heat pump operation” or “high-voltage battery  
cooling”), valves which are not open when the system is de-ener‐  
gised may be fitted in the refrigerant circuit. These valves are  
opened and closed e.g. via stepper motors and are not activated  
after the ignition is switched off. However, for the pressure in the  
refrigerant circuit to be checked when the air conditioner is switch‐  
ed off, no part of the circuit may be closed off; these valves must  
therefore be opened before performing such work ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual) and ⇒ Vehicle diagnostic tester (“Guided Fault  
Finding”).  
– Use the vehicle diagnostic tester to open the electrically acti‐  
vated valves which are not open when the system is de-  
198  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
energised ⇒ Vehicle diagnostic tester (“Guided Fault Find‐  
ing”).  
All vehicles  
– Read pressures off pressure gauges; there are two possible  
results:  
♦ The pressure in the refrigerant circuit is lower than indicated  
in the table.  
♦ The pressure in the refrigerant circuit corresponds to that in‐  
dicated in the table or is higher.  
Ambient temperature (in de‐ Pressure in refrigerant circuit in  
grees centigrade)  
+15 °C  
bar  
3.9  
4.7  
5.6  
6.7  
7.8  
9.1  
10.5  
+20 °C  
+25 °C  
+30 °C  
+35 °C  
+40 °C  
+45 °C  
Note  
♦ The temperature of the refrigerant circuit components should  
be equal to the ambient temperature. (the pressure will deviate  
from the values in the table if individual components of the  
refrigerant circuit are warmer or colder).  
♦ On the absolute pressure scale, 0 bar corresponds to an ab‐  
solute vacuum. The normal ambient pressure (atmospheric  
pressure) corresponds to 1 bar absolute pressure. On the  
scales of most pressure gauges, 0 bar corresponds to an ab‐  
solute pressure of 1 bar (can be seen from -1 bar mark below  
0).  
♦ On vehicles with a high-pressure sender - G65- , pressure  
sender for refrigerant circuit - G805- or refrigerant pressure  
and temperature sender - G395- etc. for which the measured  
pressure is displayed in the measured value block, the pres‐  
sure measured should coincide with the values in the table ⇒  
Vehicle diagnostic tester (“Self-diagnosis” or “Guided Fault  
Finding” function for air conditioner) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
♦ Pressure can be measured in various units: 1 MPa (mega‐  
pascal) is equivalent to 10 bar gauge pressure, or 145 psi; 1  
bar absolute pressure is the same as 0 bar gauge pressure,  
which is roughly equivalent to atmospheric pressure.  
The pressure in the refrigerant circuit is lower than indicated in  
the table.  
Not enough refrigerant in circuit  
– Locate leaks in refrigerant circuit ⇒ page 169 .  
– Check high-pressure safety valve.  
If the high-pressure safety valve has blown off:  
– Check actuation of the radiator fans.  
– Check for constricted refrigerant pipe and hose cross-sections  
caused by inadequate bending radii.  
8. Checking pressures  
199  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
– Check refrigerant lines and hoses for external damage.  
– If no fault is found, clean refrigerant circuit (by flushing with  
refrigerant R134a ⇒ page 100 or blowing out with compressed  
air and nitrogen ⇒ page 95 ).  
The pressure in the refrigerant circuit corresponds to that indica‐  
ted in the table or is higher.  
– Start engine or activate drive system (e.g. on vehicles with  
high-voltage system).  
– Set air conditioning system to maximum cooling output.  
Note  
♦ On vehicles with an air conditioner compressor regulating  
valve - N280- , the control current can be read out in the meas‐  
ured value block ⇒ Vehicle diagnostic tester (“Self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Air conditioner com‐  
pressor (vehicle-specific Workshop Manual).  
♦ On vehicles with an electrical air conditioner compressor -  
V470- you can read out the air conditioner compressor speed  
via different control units (e.g. via the corresponding air con‐  
ditioner control unit or the thermal management control unit -  
J1024- ) ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode.  
Vehicles with a mechanically driven air conditioner compressor  
If air conditioner compressor is not driven with engine running or  
regulating valve is not actuated:  
– Establish and eliminate the cause e.g. by interrogating the air  
conditioner event memory.  
– Observe test requirements.  
– Check the power supply for the air conditioning system mag‐  
netic clutch - N25- . If this is OK, service the magnetic clutch.  
– Check activation of air conditioner compressor regulating  
valve - N280- ⇒ Vehicle diagnostic tester (“Self-diagnosis” or  
“Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Air conditioner com‐  
pressor (vehicle-specific Workshop Manual).  
Note  
♦ If low-pressure switch has been removed to connect air con‐  
ditioner service station, jumper electrical connections in rele‐  
vant connector for pressure measurement.  
♦ Air conditioner compressor is driven by engine via air condi‐  
tioning system magnetic clutch - N25- .  
♦ The air conditioner compressor regulating valve - N280- is ac‐  
tivated by the operating and display unit for front air condition‐  
ing system - E87- or the Climatronic control unit - J255- ⇒  
Vehicle diagnostic tester (“Self-diagnosis” or “Guided Fault  
Finding” function for air conditioner) and ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
200  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Vehicles with electrical air conditioner compressor - V470- (vehi‐  
cles with high-voltage system)  
If the drive system is active but the electrical air conditioner com‐  
pressor is not activated:  
– Check activation of air conditioner compressor via corre‐  
sponding control unit ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific Workshop Manual) and  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode.  
All vehicles  
♦ Checking pressures on vehicles with a restrictor and reservoir  
(with internally regulated air conditioner compressor)  
⇒ page 201  
♦ Checking pressures on vehicles with an expansion valve and  
receiver (with internally regulated air conditioner compressor)  
⇒ page 206  
♦ Checking pressures on vehicles with restrictor, reservoir and  
air conditioner compressor regulating valve - N280- (with ex‐  
ternally regulated air conditioner compressor) ⇒ page 212  
♦ Checking pressures on vehicles with expansion valve, receiv‐  
er and air conditioner compressor regulating valve - N280-  
(with externally regulated air conditioner compressor)  
⇒ page 219  
♦ Check pressures on vehicles with electrically driven air con‐  
ditioner compressor (Audi A3 e-tron, Audi Q5 hybrid, Audi Q7  
e-tron etc.) ⇒ page 230 .  
8.2  
Checking pressures - vehicles with re‐  
strictor and reservoir (with internally  
regulated air conditioner compressor)  
Note  
♦ Connect air conditioner service station ⇒ page 187 .  
♦ Observe test requirements ⇒ page 193 .  
– Check the pressures in the refrigerant circuit (with the air con‐  
ditioner service station) with the ignition switched off  
⇒ page 195 .  
The pressures with the ignition switched off correspond to the  
specifications.  
– Start engine.  
– Set engine speed to 2000 rpm.  
– Observe the pressure reading (e.g. pressure gauge) of the air  
conditioner service station.  
8. Checking pressures  
201  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ Switching pressures for refrigerant circuit switches are vehi‐  
cle-specific.  
♦ The port with a valve for the low-pressure switch or on the  
evaporator should only be used where the vehicle does not  
have a service port on the low-pressure side and access to the  
port on the air conditioning system compressor or reservoir is  
not possible (measurement accuracy). Only applies for certain  
vehicles ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Workshop Manual).  
⇒ “8.2.1 Specifications for pressures in refrigerant circuit”,  
page 202  
8.2.1  
Specifications for pressures in refriger‐  
ant circuit  
High-pressure side:  
Increasing from initial pressure (when connecting pressure  
gauges) up to max. 20 bar  
Low-pressure side:  
Decreasing from initial pressure (on connecting pressure gauges)  
to value in graph  
A - High pressure (measured at service connection) in bar  
B - Low pressure (measured at connection with valve at air con‐  
ditioner compressor or at reservoir) in bar  
C - Permissible tolerance range  
D - Low pressure (measured at connection with valve for low-  
pressure switch or at service connection) in bar  
E - Permissible tolerance range  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
High pressure remains constant Not enough refrigerant in circuit – Localise leak with leak detector  
or only increases slightly (above  
pressure with engine stopped)  
and eliminate.  
– Re-charge refrigerant circuit.  
•
•
Low pressure quickly drops to  
value in graph or below  
Required cooling output is not at‐  
tained.  
•
•
High pressure normal  
Low pressure in line with value in  
graph  
•
Required cooling output is not at‐  
tained.  
202  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure normal  
Low pressure too low (see graph)  
Required cooling output is not at‐  
tained.  
Note  
If no fault is found for this problem, clean refrigerant circuit (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ).  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
High pressure does not rise or  
only rises slightly above the pres‐  
sure with the engine stopped.  
♦ No actuation of the air condi‐ – Check actuation and drive of the  
tioner compressor (magnetic  
clutch).  
air conditioner compressor and  
perform repair ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Air  
conditioner compressor (vehi‐  
cle-specific Workshop Manual).  
•
•
Low pressure does not drop or ♦ The air conditioner compressor  
only drops slightly.  
is not driven.  
Required cooling output is not at‐  
tained.  
♦ Constriction or blockage in re‐ – Clean refrigerant circuit (flush  
frigerant circuit (e.g. in refriger‐  
ant line between service con‐  
nection on low-pressure side  
and air conditioner compres‐  
sor).  
with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Renew hose or pipe if kinked or  
constricted.  
♦ Air conditioner compressor de‐ – Renew air conditioner compres‐  
fective sor.  
8. Checking pressures  
203  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure increases above Constriction or blockage in refrig‐ – Run hand over refrigerant circuit  
specification  
erant circuit  
to check for differences in tem‐  
perature ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Work‐  
shop Manual).  
Low pressure quickly drops to  
value in graph or below  
Required cooling output is not at‐  
tained.  
•
If there is a difference in temper‐  
ature at one component:  
– Renew hose or pipe if kinked or  
constricted.  
– In the event of clogging, clean  
refrigerant circuit (flush with re‐  
frigerant R134a ⇒ page 100 or  
blow out with compressed air  
and nitrogen ⇒ page 95 ).  
•
If no fault is found:  
– Clean refrigerant circuit (flush  
with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
•
•
•
•
High and low pressure normal at Moisture in refrigerant circuit  
first  
– Check and if necessary renew  
reservoir (with dryer) and re‐  
strictor, then evacuate refriger‐  
ant circuit for at least 3 hours  
(see note).  
High pressure rises above speci‐  
fied value  
Low pressure drops to value in  
graph or below  
– Clean refrigerant circuit (flush  
with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
Required cooling output is no lon‐  
ger attained.  
•
•
High and low pressure normal at  
first  
After lengthy operating period,  
low pressure drops excessively  
(evaporator ices up)  
Note  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer (adjust quantity of refrigerant  
oil). Subsequently, evacuate refrigerant circuit for at least 3  
hours.  
♦ It is not initially necessary to clean the refrigerant circuit (flush  
with refrigerant R134a ⇒ page 100 or blow out with com‐  
pressed air and nitrogen ⇒ page 95 ) when this problem  
occurs. Normally, there is only a small quantity of moisture in  
the system which can be removed by lengthy evacuation.  
204  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure normal  
Air conditioner compressor defective  
– Clean refrigerant cir‐  
cuit (flush with refrig‐  
erant R134a  
Low pressure too low (see graph)  
⇒ page 100 or blow  
out with compressed  
air and nitrogen  
Required cooling output is at‐  
tained.  
⇒ page 95 ).  
– Renew air condition‐  
er compressor.  
Note  
♦ Observe the following regarding fault “High pressure normal,  
low pressure too low”: This fault may cause the evaporator to  
ice up or the low-pressure switch - F73- to shut off the air con‐  
ditioner compressor although the amount of refrigerant in the  
circuit is OK.  
♦ On the Audi 100, Audi A6 (up to and including model year  
1997) and Audi V8, this fault may result in the air conditioner  
compressor being shut off by the operating and display unit (if  
the temperature at the fresh air blower drops below -3 °C) ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual) or ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Overview of fitting locations - air conditioner  
(vehicle-specific Workshop Manual).  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
•
High pressure normal or too high Too much refrigerant in circuit  
– Extract refrigerant  
from refrigerant cir‐  
cuit.  
Low pressure too high (see  
graph)  
•
If quantity of refriger‐  
ant extracted roughly  
corresponds to  
•
•
Noise from air conditioner com‐  
pressor (particularly after being  
switched on)  
specified capacity:  
Required cooling output is not at‐  
tained.  
– Renew air condition‐  
er compressor.  
•
The quantity of re‐  
frigerant extracted is  
significantly greater  
than the prescribed  
charge quantity.  
– Re-charge refriger‐  
ant circuit.  
– Repeat test.  
8. Checking pressures  
205  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from specification  
Possible causes of fault  
Fault elimination  
•
•
High and low pressure normal  
Too much refrigerant oil in circuit  
– Discharge refriger‐  
ant circuit.  
Required cooling output is not at‐  
tained.  
– Clean refrigerant  
circuit (flush with re‐  
frigerant R134a  
⇒ page 100 or blow  
out with com‐  
pressed air and ni‐  
trogen ⇒ page 95 ).  
•
•
High and low pressure normal  
Noise from air conditioner com‐  
pressor (particularly after being  
switched on)  
•
Required cooling output is at‐  
tained.  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flush with refrigerant R134a  
⇒ page 100 or blow out with compressed air and nitrogen  
⇒ page 95 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
8.3  
Checking pressures - vehicles with ex‐  
pansion valve and receiver (with inter‐  
nally regulated air conditioner compres‐  
sor)  
Note  
♦ Connect air conditioner service station ⇒ page 187 .  
♦ Observe test requirements ⇒ page 193 .  
– Check the pressures in the refrigerant circuit (with the air con‐  
ditioner service station) with the ignition switched off  
⇒ page 195 .  
The pressures with the ignition switched off correspond to the  
specifications.  
– Start engine.  
– Set engine speed to 2000 rpm.  
– Observe the pressure reading (e.g. pressure gauge) of the air  
conditioner service station.  
206  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ Switching pressures and design of refrigerant circuit switches  
are vehicle-specific.  
♦ Measure the pressures at the service connections; the fitting  
locations of these connections are vehicle-specific ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
⇒ “8.3.1 Specifications for pressures in refrigerant circuit”,  
page 207  
8.3.1  
Specifications for pressures in refriger‐  
ant circuit  
High-pressure side:  
Increasing from initial pressure (when connecting pressure  
gauges) up to max. 20 bar  
Low-pressure side:  
Decreasing from initial pressure (on connecting pressure gauges)  
to value in graph  
A - High pressure in bar  
B - Low pressure in bar  
C - Permissible tolerance range  
Possible deviation from  
specification  
Possible causes of fault  
Fault elimination  
•
High pressure remains Not enough refrigerant in circuit or – Extract refrigerant from refrigerant cir‐  
constant or only increa‐ expansion valve defective  
cuit.  
ses slightly (above pres‐  
sure with engine stop‐  
ped)  
•
If quantity of refrigerant extracted rough‐  
ly corresponds to specified capacity:  
•
•
Low pressure quickly  
drops to value in graph  
or below  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Required cooling output  
is not attained.  
•
The quantity of refrigerant extracted is  
substantially less than the specified ca‐  
pacity.  
•
•
High pressure normal  
Low pressure in line with  
value in graph  
– Locate leak with leak detector and repair  
it.  
•
Required cooling output  
is not attained.  
– Re-charge refrigerant circuit.  
– Repeat test.  
8. Checking pressures  
207  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
If no fault can be found and air conditioner operation is not OK  
when the test is repeated, clean the refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or blow out with compressed air  
and nitrogen ⇒ page 95 ).  
Possible devia‐ Possible causes of  
Fault elimination  
tion from speci‐  
fication  
fault  
•
High pres‐ ♦ No actuation of – Check actuation and  
sure does  
not rise or  
only rises  
slightly  
the air condition‐  
er compressor  
(magnetic  
drive of the air condi‐  
tioner compressor  
and perform repair ⇒  
Heating, air condi‐  
tioning; Rep. gr. 87 ;  
Air conditioner com‐  
pressor (vehicle-spe‐  
cific Workshop Man‐  
ual).  
clutch)  
above the  
pressure  
with the en‐  
gine stop‐  
ped.  
♦ The air condi‐  
tioner compres‐  
sor is not driven.  
•
•
Low pres‐  
sure does  
not drop or  
only drops  
slightly.  
Required  
cooling out‐  
put is not at‐  
tained.  
♦ Constriction or – Clean refrigerant cir‐  
blockage in re‐  
frigerant circuit  
(e.g. in refriger‐  
ant line between  
service connec‐  
tion on low-pres‐  
sure side and air  
cuit (flush with refrig‐  
erant R134a  
⇒ page 100 or blow  
out with compressed  
air and nitrogen  
⇒ page 95 ).  
conditioner com‐ – Renew hose or pipe if  
pressor).  
kinked or constricted.  
♦ Air conditioner  
compressor de‐  
fective  
– Renew air condition‐  
er compressor.  
208  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from  
specification  
Possible causes of fault  
Fault elimination  
•
•
High pressure increases ♦ Constriction or blockage in refriger‐ – Run hand over refrigerant circuit to  
above specification  
ant circuit  
check for differences in tempera‐  
ture ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit;  
System overview - refrigerant cir‐  
cuit (vehicle-specific Workshop  
Manual).  
Low pressure quickly  
drops to value in graph  
or below  
♦ Expansion valve defective  
•
Required cooling output  
is not attained.  
•
If there is a difference in tempera‐  
ture at one component:  
– Renew hose or pipe if kinked or  
constricted.  
– In the event of clogging, clean re‐  
frigerant circuit (flush with refriger‐  
ant R134a ⇒ page 100 or blow out  
with compressed air and nitrogen  
⇒ page 95 and renew expansion  
valve if applicable).  
•
If no fault is found:  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and  
nitrogen ⇒ page 95 and renew ex‐  
pansion valve if applicable).  
– Repeat test.  
Note  
If operation is not OK after cleaning the refrigerant circuit (flushing  
with refrigerant R134a ⇒ page 100 or blowing out with com‐  
pressed air and nitrogen ⇒ page 95 ), renew the expansion valve.  
Possible deviation from  
specification  
Possible causes of fault  
Fault elimination  
•
•
High and low pressure ♦ Expansion valve defective  
– Renew receiver (with dryer) and  
evacuate refrigerant circuit for at  
least 3 hours (see notes).  
normal at first  
♦ Moisture in refrigerant circuit  
After some time, high  
pressure increases  
– Check expansion valve for dirt or  
corrosion and renew if necessary  
above specification and  
low pressure drops to  
value in graph or below  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and  
nitrogen ⇒ page 95 ).  
•
Required cooling output  
is no longer attained.  
•
•
High and low pressure  
normal at first  
After lengthy operating  
period, low pressure  
drops excessively  
(evaporator ices up)  
8. Checking pressures  
209  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ It is not initially necessary to clean the refrigerant circuit (flush  
with refrigerant R134a ⇒ page 100 or blow out with com‐  
pressed air and nitrogen ⇒ page 95 ) when this problem  
occurs. Normally, there is only a small quantity of moisture in  
the system which can be removed by lengthy evacuation.  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer (adjust quantity of refrigerant  
oil). Subsequently, evacuate refrigerant circuit for at least 3  
hours.  
Possible deviation from specifica‐  
tion  
Possible causes of fault  
Fault elimination  
•
•
•
•
High pressure normal or too  
high  
♦ Too much refrigerant in circuit – Extract refrigerant from refrigerant  
circuit.  
♦ Expansion valve or air condi‐  
Low pressure too high (see  
graph)  
tioner compressor defective.  
•
If amount of refrigerant extracted  
roughly corresponds to specified  
capacity:  
Required cooling output is not  
attained  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Air conditioner compressor  
noise (particularly after switch-  
on).  
•
The quantity of refrigerant extrac‐  
ted is significantly greater than the  
prescribed charge quantity.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
If operation of the air conditioning system is not OK when the test  
is repeated, re-fit the old expansion valve and clean the refriger‐  
ant circuit (flush with refrigerant R134a ⇒ page 100 or blow out  
with compressed air and nitrogen ⇒ page 95 ). Then renew the  
air conditioner compressor and receiver.  
Possible deviation from specifica‐  
tion  
Possible causes of fault  
Fault elimination  
•
High pressure only increases Air conditioner compressor de‐ – Clean refrigerant circuit (flush with  
slightly above pressure with  
engine stopped  
fective  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and  
nitrogen ⇒ page 95 ).  
•
•
Low pressure only drops slight‐  
ly  
– Renew the air conditioner com‐  
pressor and receiver.  
Required cooling output is not  
attained.  
210  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from specifica‐  
tion  
Possible causes of fault  
Fault elimination  
•
High pressure normal  
Expansion valve or air condition‐ – Renew expansion valve.  
er compressor defective.  
•
Low pressure too low (see  
graph)  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
Required cooling output is at‐  
tained.  
Note  
♦ If operation of the air conditioning system is not OK when the  
test is repeated, re-fit the old expansion valve and clean the  
refrigerant circuit (flush with refrigerant R134a ⇒ page 100 or  
blow out with compressed air and nitrogen ⇒ page 95 ). Then  
renew the air conditioner compressor and receiver.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
Possible deviation from specifica‐  
tion  
Possible causes of fault  
Fault elimination  
•
•
High and low pressure normal Too much refrigerant oil in circuit – Discharge refrigerant circuit.  
Required cooling output is not  
attained.  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and  
nitrogen ⇒ page 95 ).  
•
•
High and low pressure normal  
Noise from air conditioner com‐  
pressor (particularly after being  
switched on)  
•
Required cooling output is at‐  
tained.  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flush with refrigerant R134a  
⇒ page 100 or blow out with compressed air and nitrogen  
⇒ page 95 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
8. Checking pressures  
211  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
8.4  
Checking pressures - vehicles with re‐  
strictor, reservoir and air conditioner  
compressor regulating valve - N280-  
(with externally regulated air conditioner  
compressor)  
Note  
♦ Connect air conditioner service station ⇒ page 187 .  
♦ Observe test requirements ⇒ page 193 .  
– Check the pressures in the refrigerant circuit (with the air con‐  
ditioner service station) with the ignition switched off  
⇒ page 195 .  
The pressures with the ignition switched off correspond to the  
specifications.  
– Start engine.  
– Set engine speed to 2000 rpm.  
– Observe the pressure reading (e.g. pressure gauge) of the air  
conditioner service station.  
Note  
♦ The switching pressures for actuation of -N280- and the radi‐  
ator fans - V7- are vehicle-specific.  
♦ Measure the pressures at the service connections; the fitting  
locations of these connections are vehicle-specific ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
⇒ “8.4.1 Specifications for pressures in refrigerant circuit”,  
page 212  
8.4.1  
Specifications for pressures in refriger‐  
ant circuit  
High-pressure side:  
Increasing from initial pressure (on connection of pressure  
gauges) up to 20 bar  
212  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Low-pressure side:  
Decreasing from initial pressure (on connecting pressure gauges)  
to value in graph  
A - Low pressure (measured at service connection) in bar abso‐  
lute pressure.  
B - Control current for air conditioner compressor regulating valve  
- N280- in amps  
C - Permissible tolerance range  
8. Checking pressures  
213  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ In the event of a very high cooling output requirement (e.g.  
high ambient temperature and high fresh air blower speed at  
low engine speed), the air conditioner compressor cannot in‐  
itially set the pressure on the low-pressure end to the value  
-C- given in the graph (e.g. for a certain time after switching  
on the air conditioner). The air conditioner compressor is ac‐  
tuated with the maximum specified control current, however  
the delivery volume of the air conditioner compressor is no  
longer sufficient under these ambient conditions and at this  
engine speed to reduce the pressure on the low-pressure end  
to the value in the graph. One way of checking the control ac‐  
tion of the air conditioner compressor under these conditions  
is to activate 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 (“self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output or ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐  
ual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high humidity), pressure on high-pressure end may  
increase to max. 29 bar.  
♦ Control current -B- is displayed in measured value block of  
operating and display unit for front air conditioning system -  
E87- or operating and display unit ( Climatronic control unit -  
J255- ).  
♦ The pressure in the refrigerant circuit measured by the high-  
pressure sender - G65- or the refrigerant pressure and tem‐  
perature sender - G395- is displayed in the measured value  
block of -E87- or of the operating and display unit ( Climatronic  
control unit - J255- ) ⇒ Vehicle diagnostic tester (“Self-diag‐  
nosis” or “Guided Fault Finding” function for air conditioner)  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Workshop Manual).  
♦ The low pressure settles as a function of the control current  
for the air conditioner compressor regulating valve - N280-  
within the air conditioner compressor output range in the tol‐  
erance band.  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high humidity), the air conditioner compressor output  
may not always be sufficient to attain the specified value.  
♦ If the compressor capacity utilisation is greater than 90 %, the  
pressure on the low-pressure end may be in excess of the  
tolerance range “C” shown in the graph (the compressor out‐  
put no longer suffices).  
♦ The specified operating current for the regulating valve must  
be greater than 0.3 A to ensure reliable actuation of the regu‐  
lating valve.  
♦ “0 bar absolute pressure” corresponds to an absolute vacuum.  
Normal ambient pressure corresponds to an absolute pres‐  
sure of 1 bar. On the scales of most pressure gauges, 0 bar  
corresponds to an absolute pressure of one bar (can be seen  
from “-1 bar” mark below “0”).  
214  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ In the "maximum cooling output" setting, the control current is  
regulated to approx. 0.65 (up to 0.85 A for specific vehicles);  
this is displayed in the measured value block ⇒ Vehicle diag‐  
nostic tester (“Self-diagnosis” or “Guided Fault Finding” func‐  
tion for air conditioner) and ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Repair instructions; Checking cooling output or ⇒  
Heating, air conditioning; Rep. gr. 87 ; Overview of fitting lo‐  
cations - air conditioner (vehicle-specific Workshop Manual).  
Possible deviation from  
specification  
Possible causes of fault  
Fault elimination  
•
High pressure remains  
constant or only increa‐  
ses slightly (above pres‐  
sure with engine stop‐  
ped)  
♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐  
pressor regulating valve - N280-  
not OK  
ing, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific  
Workshop Manual).  
♦ Not enough refrigerant in circuit  
– Locate leak with leak detector and  
repair it.  
•
•
Low pressure quickly  
drops to value in graph or  
below  
– Re-charge refrigerant circuit.  
Required cooling output  
is not attained.  
•
•
High pressure normal  
Low pressure too low  
(see graph)  
•
Required cooling output  
is not attained.  
Note  
If no fault is found for this problem, clean refrigerant circuit (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ).  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
High pressure does not  
rise or only rises slightly  
above the pressure with  
the engine stopped.  
♦ No actuation of the air conditioner – Check actuation and drive of the air  
compressor ( air conditioner  
compressor regulating valve -  
N280- )  
conditioner compressor and perform  
repair ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air conditioner com‐  
pressor (vehicle-specific Workshop  
Manual).  
•
•
Low pressure does not  
♦ The air conditioner compressor is  
not driven.  
drop or only drops slightly.  
– Check actuation and operation of -  
N280- .  
Required cooling output is  
not attained.  
♦ Constriction or blockage in refrig‐ – Clean refrigerant circuit (flush with  
erant circuit (e.g. in refrigerant  
line between service connection  
on low-pressure side and air con‐  
ditioner compressor).  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and ni‐  
trogen ⇒ page 95 ).  
– Renew hose or pipe if kinked or con‐  
stricted.  
♦ Air conditioner compressor regu‐ – Check operation of -N280- , remove  
lating valve - N280- defective  
-N280- if applicable and check for  
contamination ⇒ page 285 .  
8. Checking pressures  
215  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from spec‐  
Possible causes of fault  
Fault elimination  
ification  
♦ Air conditioner compressor de‐ – Renew air conditioner compressor.  
fective  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
High pressure increases ♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐  
above specification  
Low pressure quickly  
pressor regulating valve - N280-  
not OK  
ing, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific  
Workshop Manual).  
•
drops to value in graph or ♦ Constriction or blockage in refrig‐  
below  
erant circuit  
– Run hand over refrigerant circuit to  
check for differences in temperature.  
•
Required cooling output is  
not attained.  
•
If there is a difference in temperature  
at one component:  
– Renew hose or pipe if kinked or con‐  
stricted.  
– Flush the refrigerant circuit with com‐  
pressed air and nitrogen in the event  
of an obstruction.  
•
If no fault is found:  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and ni‐  
trogen ⇒ page 95 ).  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
High and low pressure  
normal at first, after some  
time high pressure increa‐  
ses above specification  
and  
♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐  
pressor regulating valve - N280-  
not OK  
ing, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific  
Workshop Manual).  
– Renew reservoir (with dryer) and  
evacuate refrigerant circuit for at  
least 3 hours (see note).  
•
•
Low pressure drops to val‐  
ue in graph or below  
Required cooling output is  
no longer attained.  
♦ Air conditioner compressor regu‐ – Check operation of -N280- , remove  
•
•
High and low pressure  
normal at first  
lating valve - N280- defective  
-N280- if applicable and check for  
contamination ⇒ page 285 .  
After lengthy operating pe‐  
riod, low pressure drops  
excessively (evaporator  
ices up)  
♦ Moisture in refrigerant circuit  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and ni‐  
trogen ⇒ page 95 ).  
216  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ It is not initially necessary to clean the refrigerant circuit (flush  
with refrigerant R134a ⇒ page 100 or blow out with com‐  
pressed air and nitrogen ⇒ page 95 ) when this problem  
occurs. Normally, there is only a small quantity of moisture in  
the system which can be removed by lengthy evacuation.  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer (adjust quantity of refrigerant  
oil). Subsequently, evacuate refrigerant circuit for at least 3  
hours.  
♦ A problem with evaporator output temperature sender - G263-  
can also cause icing-up of refrigerant circuit. If this problem  
occurs, you should also check the measured value of the  
evaporator output temperature sender - G263- ⇒ Vehicle di‐  
agnostic tester (“Self-diagnosis” or “Guided Fault Finding”  
function for air conditioner) and ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output or  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
•
High pressure normal  
♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐  
pressor regulating valve - N280-  
not OK  
ing, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific  
Workshop Manual).  
Low pressure too low (see  
graph)  
♦ Air conditioner compressor regu‐  
lating valve - N280- defective  
•
Required cooling output is  
attained.  
– Check operation of -N280- , remove  
-N280- if applicable and check for  
contamination ⇒ page 285 .  
♦ Air conditioner compressor de‐ – Clean refrigerant circuit (flush with  
fective  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and  
nitrogen ⇒ page 95 ).  
– Renew air conditioner compressor.  
Note  
Observe the following regarding fault “High pressure normal, low  
pressure too low”: This fault may cause the evaporator to ice up  
although the amount of refrigerant in the circuit is OK. Check  
measured values of evaporator output temperature sender -  
G263- and actuation of air conditioner compressor regulating  
valve - N280- . If the measured value of the evaporator output  
temperature sender - G263- is incorrect, the evaporator may ice  
up or the cooling output may not be attained ⇒ Vehicle diagnostic  
tester (“Self-diagnosis” or “Guided Fault Finding” function for air  
conditioner) and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking cooling output or ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Workshop  
Manual).  
8. Checking pressures  
217  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure normal or ♦ Actuation of air conditioner compressor – Check activation of -N280- ⇒  
too high  
regulating valve - N280- not OK  
♦ Too much refrigerant in circuit  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
Low pressure too high  
(see graph)  
Noise from air conditioner  
compressor (particularly  
after being switched on)  
– Extract refrigerant from refrig‐  
erant circuit.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
•
Required cooling output is  
not attained.  
– Renew air conditioner com‐  
pressor.  
•
The quantity of refrigerant ex‐  
tracted is significantly greater  
than the prescribed charge  
quantity.  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
•
High and low pressure  
normal  
♦ Actuation of air conditioner compressor – Check actuation of -N280- .  
regulating valve - N280- not OK  
– Discharge refrigerant circuit.  
Required cooling output is ♦ Too much refrigerant oil in circuit  
not attained.  
– Clean refrigerant circuit (flush  
with refrigerant R134a  
•
•
High and low pressure  
normal.  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
Air conditioner compres‐  
sor noise (particularly after  
switch-on).  
•
Required cooling output is  
attained.  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flush with refrigerant R134a  
⇒ page 100 or blow out with compressed air and nitrogen  
⇒ page 95 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
218  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
8.5  
Checking pressures - vehicles with ex‐  
pansion valve, receiver and air condi‐  
tioner compressor regulating valve -  
N280- (with externally regulated air  
conditioner compressor)  
Note  
♦ Connect air conditioner service station ⇒ page 187 .  
♦ Observe test requirements ⇒ page 193 .  
♦ If problems are only encountered at one evaporator on vehi‐  
cles fitted with two evaporators, check whether the pressures  
in the refrigerant circuit are OK. Check for cross-sectional re‐  
striction or blockage of line connection between faulty evapo‐  
rator and outgoing line connection at refrigerant line distribu‐  
tion point. If no fault is found, discharge the refrigerant circuit  
and re-fill it with the specified quantity of refrigerant. Then  
check the pressures and the cooling output of the air condi‐  
tioner again. If the problem persists, renew the expansion  
valve upstream of the faulty evaporator ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Work‐  
shop Manual).  
– Check the pressures in the refrigerant circuit (with the air con‐  
ditioner service station) with the ignition switched off  
⇒ page 195 .  
The pressures with the ignition switched off correspond to the  
specifications.  
– Start engine.  
– Set engine speed to 2000 rpm.  
– Observe the pressure reading (e.g. pressure gauge) of the air  
conditioner service station.  
Note  
♦ The switching pressures for actuation of the air conditioner  
compressor regulating valve - N280- and the radiator fans -  
V7- are vehicle-specific.  
♦ Measure the pressures at the service connections; the fitting  
locations of these connections are vehicle-specific ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
⇒ “8.5.1 Specifications for pressures in refrigerant circuit”,  
page 219  
8.5.1  
Specifications for pressures in refriger‐  
ant circuit  
High-pressure side:  
Increasing from initial pressure (when connecting pressure  
gauges) up to max. 20 bar  
8. Checking pressures  
219  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Low pressure:  
Decreasing from initial pressure (on connecting pressure gauges)  
to value in graph  
A - Low pressure (measured at service connection) in bar abso‐  
lute pressure.  
B - Control current for air conditioner compressor regulating valve  
- N280- in amps  
C - Permissible tolerance range (applicable to compressor ca‐  
pacity utilisation of 10...90 %).  
220  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ In the event of a very high cooling output requirement (e.g.  
high ambient temperature and high fresh air blower speed at  
low engine speed), the air conditioner compressor cannot in‐  
itially set the pressure on the low-pressure end to the value  
-C- given in the graph (e.g. for a certain time after switching  
on the air conditioner). The air conditioner compressor is ac‐  
tuated with the maximum specified control current, however  
the delivery volume of the air conditioner compressor is no  
longer sufficient under these ambient conditions and at this  
engine speed to reduce the pressure on the low-pressure end  
to the value in the graph. One way of checking the control ac‐  
tion of the air conditioner compressor under these conditions  
is to activate 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 (“self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output or ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐  
ual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high humidity), the pressure on the high-pressure side  
may increase to max. 29 bar.  
♦ Control current -B- is displayed in measured value block of  
operating and display unit for front air conditioning system -  
E87- or Climatronic control unit - J255- .  
♦ High pressure measured by the high-pressure sender - G65-  
(or refrigerant pressure and temperature sender - G395- /  
pressure sender for refrigerant circuit - G805- ) is displayed as  
a measured value of -E87- or of the air conditioning system  
control unit - J301- / operating and display unit ( Climatronic  
control unit - J255- ).  
♦ The low pressure settles as a function of the control current  
for the air conditioner compressor regulating valve - N280- and  
the control characteristic of the expansion valve within the air  
conditioner compressor output range in the tolerance band.  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high humidity), the air conditioner compressor output  
may not always be sufficient to attain the specified value.  
♦ If the compressor capacity utilisation is greater than 90 %, the  
pressure on the low-pressure end may be in excess of the  
tolerance range “C” shown in the graph (the compressor out‐  
put no longer suffices).  
♦ The specified operating current for the air conditioner com‐  
pressor regulating valve - N280- must be greater than 0.3 A to  
ensure reliable valve actuation.  
♦ In the “maximum cooling output” setting, the control current for  
the air conditioner compressor regulating valve - N280- is  
regulated to approx. 0.65 A (up to 0.85 A). This measured val‐  
ue is vehicle-specific and displayed in the measured value  
block.  
8. Checking pressures  
221  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ On the absolute pressure scale, 0 bar corresponds to an ab‐  
solute vacuum. Normal ambient pressure corresponds to an  
absolute pressure of 1 bar. On the scale 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 (“Self-diagnosis” or “Guided Fault Finding” function for  
air conditioner) and ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output or ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure remains con‐ ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒  
stant or only increases  
slightly (above pressure  
with engine stopped)  
sor regulating valve - N280- not OK  
♦ Not enough refrigerant in circuit  
♦ Expansion valve defective  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
•
•
Low pressure quickly drops  
to value in graph or below  
– Extract refrigerant from re‐  
frigerant circuit.  
Required cooling output is  
not attained.  
•
If quantity of refrigerant ex‐  
tracted is substantially less  
than specified capacity:  
– Locate leak with leak detec‐  
tor and repair it.  
•
•
High pressure normal  
Low pressure in line with  
value in graph  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
Required cooling output is  
not attained.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
•
•
High pressure normal  
Low pressure too low (see  
graph)  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
Required cooling output is  
not attained.  
222  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If no fault is found for this problem, clean refrigerant circuit (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ).  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of -N280- . If the measured  
value of the evaporator output temperature sender - G263- is  
not OK, the evaporator may ice up or the cooling output is not  
attained.  
♦ If, after renewing the expansion valve, operation of the air  
conditioning system is not OK when the test is repeated (re-fit  
old expansion valve), clean the refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or blow out with compressed air  
and nitrogen ⇒ page 95 ). Then renew the air conditioner com‐  
pressor and receiver.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ If the expansion valve is defective (permanently closed or  
does not open sufficiently), -N280- is actuated to maximum  
output and the low pressure drops to the value in the graph or  
below (the air conditioner compressor draws off refrigerant  
from the low-pressure end). However, as refrigerant cannot  
flow via the expansion valve, the cooling output is not attained  
and the high pressure may also not increase or only increase  
slightly since there is no energy exchange ⇒ Vehicle diag‐  
nostic tester (“Self-diagnosis” or “Guided Fault Finding” func‐  
tion for air conditioner) and ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Repair instructions; Checking cooling output or ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
Possible devia‐ Possible causes of  
Fault elimination  
tion from specifi‐  
cation  
fault  
•
High pres‐  
sure does not  
rise or only  
rises slightly  
above the  
♦ No actuation of – Check actuation  
the air condition‐  
er compressor  
( air conditioner  
compressor regu‐  
lating valve -  
and drive of the air  
conditioner com‐  
pressor and per‐  
form repair ⇒ Heat‐  
ing, air condition‐  
ing; Rep. gr. 87 ; Air  
conditioner com‐  
pressor (vehicle-  
specific Workshop  
Manual).  
pressure with  
the engine  
stopped.  
N280- )  
♦ The air condition‐  
er compressor is  
not driven.  
•
•
Low pressure  
does not drop  
or only drops  
slightly.  
Required  
cooling out‐  
put is not at‐  
tained.  
♦ Air conditioner  
compressor regu‐  
lating valve -  
– Check operation of  
-N280- , remove -  
N280- if applicable  
and check for con‐  
tamination  
N280- defective.  
⇒ page 285 .  
8. Checking pressures  
223  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible devia‐ Possible causes of  
Fault elimination  
tion from specifi‐  
cation  
fault  
♦ Constriction or  
blockage in re‐  
frigerant circuit  
(e.g. in refrigerant  
line between  
– Clean refrigerant  
circuit (flush with re‐  
frigerant R134a  
⇒ page 100 or blow  
out with com‐  
service connec‐  
tion on low-pres‐  
sure side and air  
pressed air and ni‐  
trogen ⇒ page 95 ).  
conditioner com‐ – Renew hose or pipe  
pressor).  
if kinked or constric‐  
ted.  
♦ Air conditioner  
compressor de‐  
fective  
– Renew air condi‐  
tioner compressor.  
Note  
♦ In the event of this problem, make sure the air conditioner  
compressor (air conditioner compressor shaft) is actually be‐  
ing driven via the pulley/drive unit ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Air conditioner compressor (vehicle-specific  
Workshop Manual).  
♦ As of Model Year 2012, air conditioner compressors with both  
-N280- and an air conditioning system magnetic clutch - N25-  
fitted at the pulley are to be introduced for certain engines and  
models. In the event of this problem, make sure -N25- is ac‐  
tually being actuated and that the air conditioner compressor  
(air conditioner compressor shaft) is being driven via the pulley  
⇒ Heating, air conditioning; Rep. gr. 87 ; Air conditioner com‐  
pressor (vehicle-specific Workshop Manual) and ⇒ Electronic  
parts catalogue .  
224  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure increases ♦ Actuation of air conditioner com‐ – Check activation of -N280- ⇒ Heat‐  
above specification  
pressor regulating valve - N280-  
not OK  
ing, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific  
Workshop Manual).  
Low pressure quickly  
drops to value in graph  
♦ Constriction or blockage in refrig‐  
erant circuit  
– Run hand over refrigerant circuit to  
check for differences in temperature.  
Required cooling output is  
not attained.  
♦ Expansion valve defective  
•
If there is a difference in temperature  
at one component:  
– Renew hose or pipe if kinked or con‐  
stricted.  
– In the event of clogging, clean refrig‐  
erant circuit (flush with refrigerant  
R134a ⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
If no fault is found:  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and ni‐  
trogen ⇒ page 95 ).  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not OK:  
– Renew expansion valve and receiv‐  
er.  
8. Checking pressures  
225  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If the function of the air conditioning system is not OK when  
the test is repeated, renew expansion valve and receiver.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ If the expansion valve is defective (permanently closed or  
does not open sufficiently), the air conditioner compressor  
regulating valve - N280- is actuated to maximum output and  
the low pressure drops to the value in the graph or below (the  
air conditioner compressor draws off refrigerant from the low-  
pressure end). However, as refrigerant cannot flow via the  
expansion valve, the cooling output is not attained and the high  
pressure may also not increase or only increase slightly since  
there is no energy exchange ⇒ Vehicle diagnostic tester  
(“Self-diagnosis” or “Guided Fault Finding” function for air con‐  
ditioner) and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking cooling output or ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Work‐  
shop Manual).  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flush with refrigerant R134a  
⇒ page 100 or blow out with compressed air and nitrogen  
⇒ page 95 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
•
•
•
High and low pressure nor‐ ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒  
mal at first, but after a while:  
sor regulating valve - N280- not OK  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
High pressure rises above ♦ Moisture in refrigerant circuit  
specified value  
Low pressure drops to val‐  
ue in graph or below  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
Required cooling output is  
no longer attained.  
– Renew receiver with dryer.  
•
•
High and low pressure nor‐  
mal at first  
– Evacuate refrigerant circuit  
for at least 3 hours.  
After lengthy driving time,  
low pressure drops below  
specification (evaporator  
ices up)  
– Re-charge refrigerant circuit.  
– Repeat test.  
♦ Air conditioner compressor regulating – Check operation of -N280- ,  
valve - N280- defective  
remove -N280- if applicable  
and check for contamination  
⇒ page 285 .  
226  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ It is not initially necessary to clean the refrigerant circuit (flush  
with refrigerant R134a ⇒ page 100 or blow out with com‐  
pressed air and nitrogen ⇒ page 95 ) when this problem  
occurs. Normally, there is only a small quantity of moisture in  
the system which can be removed by lengthy evacuation.  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer in the receiver (adjust quantity  
of refrigerant oil). Subsequently, evacuate refrigerant circuit  
for at least 3 hours.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ A problem with evaporator output temperature sender - G263-  
can also cause icing-up of refrigerant circuit. If this problem  
occurs, you should also check the measured value of the  
evaporator output temperature sender - G263- ⇒ Vehicle di‐  
agnostic tester (“Self-diagnosis” or “Guided Fault Finding”  
function for air conditioner) and ⇒ Heating, air conditioning;  
Rep. gr. 00 ; Repair instructions; Checking cooling output or  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure normal  
♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒  
sor regulating valve - N280- not OK  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
•
Low pressure too low (see  
graph)  
•
Required cooling output is  
attained.  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ) (not always nec‐  
essary, refer to notes).  
♦ Air conditioner compressor regulating – Check operation of -N280- ,  
valve - N280- defective  
remove -N280- if applicable  
and check for contamination  
⇒ page 285 .  
♦ Expansion valve or air conditioner  
compressor defective.  
– Renew expansion valve and  
receiver.  
♦ Air conditioner compressor defective  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
– Renew air conditioner com‐  
pressor.  
– Re-charge refrigerant circuit.  
– Repeat test.  
8. Checking pressures  
227  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ Observe the following regarding fault “High pressure normal,  
low pressure too low”: This fault may cause the evaporator to  
ice up although the amount of refrigerant in the circuit is OK.  
♦ If the problem is with -N280- (the regulating valve is not actu‐  
ated but the air conditioner compressor operates neverthe‐  
less), the refrigerant circuit does not have to be cleaned (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ). 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 (permanently closed or  
does not open sufficiently), -N280- is actuated to maximum  
output and the low pressure drops to the value in the graph or  
below (the air conditioner compressor draws off refrigerant  
from the low-pressure end). As refrigerant cannot however  
flow via expansion valve, cooling output is not attained and  
high pressure may either not increase or only slightly due to  
the absence of energy conversion.  
♦ Check the measured values of the evaporator output temper‐  
ature sender - G263- and actuation of -N280- . If the measured  
value of the evaporator output temperature sender - G263- is  
incorrect, the evaporator may ice up or the cooling output may  
not be attained ⇒ Vehicle diagnostic tester (“Self-diagnosis”  
or “Guided Fault Finding” function for air conditioner) and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output or ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐  
ual).  
228  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure normal or too ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒  
high  
sor regulating valve - N280- not OK  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
Low pressure too high (see ♦ Too much refrigerant in circuit  
graph)  
♦ Expansion valve defective  
Noise from air conditioner  
– Extract refrigerant from re‐  
frigerant circuit.  
♦ Air conditioner compressor defective  
compressor (particularly af‐  
ter being switched on)  
•
The quantity of refrigerant  
extracted corresponds  
roughly to the actual capaci‐  
ty.  
•
Required cooling output is  
attained.  
– Renew expansion valve and  
receiver.  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
– Renew air conditioner com‐  
pressor.  
•
If quantity of refrigerant ex‐  
tracted is significantly great‐  
er than specified capacity:  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
♦ This fault may also be caused by too much refrigerant oil in  
the circuit. Overfilling with refrigerant oil may occur if, for ex‐  
ample, the air conditioner compressor has been renewed  
without adjusting the quantity of refrigerant oil.  
♦ If the expansion valve is defective (permanently closed or  
does not open sufficiently), -N280- is actuated to maximum  
output and the low pressure drops to the value in the graph or  
below (the air conditioner compressor draws off refrigerant  
from the low-pressure end). However, as refrigerant cannot  
flow via the expansion valve, the cooling output is not attained  
and the high pressure may also not increase or only increase  
slightly since there is no energy exchange ⇒ Vehicle diag‐  
nostic tester (“Self-diagnosis” or “Guided Fault Finding” func‐  
tion for air conditioner) and ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Repair instructions; Checking cooling output or ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
8. Checking pressures  
229  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High and low pressure nor‐ ♦ Actuation of air conditioner compres‐ – Check activation of -N280- ⇒  
mal  
sor regulating valve - N280- not OK  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
•
Required cooling output is ♦ Too much refrigerant in circuit  
attained.  
♦ Expansion valve defective  
– Discharge refrigerant circuit.  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Add correct quantity of refrig‐  
erant oil to circuit (refer to  
note).  
•
•
High and low pressure nor‐  
mal  
Noise from air conditioner  
compressor (particularly af‐  
ter being switched on)  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
•
Required cooling output is  
attained.  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If the expansion valve is defective (permanently open), the  
evaporator temperature is no longer regulated such that only  
refrigerant in gas form exits from the evaporator. Under certain  
usage conditions, liquid droplets may then be drawn in by the  
air conditioner compressor and result in noise (liquid cannot  
be compressed).  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flush with refrigerant R134a  
⇒ page 100 or blow out with compressed air and nitrogen  
⇒ page 95 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
8.6  
Checking pressures - vehicles with electrically driven air conditioner com‐  
pressor (vehicles with high-voltage system)  
High voltage! Danger to life!  
The voltage levels in the high-voltage system constitute a safety  
hazard. Danger of severe or fatal injuries from electric shock.  
– Persons with life-sustaining or other electronic medical devi‐  
ces in or on their body must not perform any work on the high-  
voltage system. Such medical devices include internal anal‐  
gesic pumps, implanted defibrillators, pacemakers, insulin  
pumps and hearing aids.  
230  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
– The high-voltage system must be de-energised by a suitably  
qualified person.  
Risk of injury - engine may start unexpectedly  
It is difficult to determine whether the drive system of an electric  
vehicle or hybrid vehicle is active. Moving parts can trap or draw  
in parts of the body.  
– Switch off ignition.  
– Place ignition key outside vehicle.  
Risk of damage to high-voltage wiring  
Incorrect handling may result in damage to the insulation of high-  
voltage wires or high-voltage connectors.  
– Never use high-voltage wiring or high-voltage connectors as  
a support.  
– Never prop tools against high-voltage wiring or high-voltage  
connectors.  
– Never bend or kink high-voltage wiring.  
– Pay attention to coding when connecting high-voltage con‐  
nections.  
♦ For all work on vehicles with high-voltage system, note addi‐  
tional warnings for working on such vehicles  
⇒ “1 Warning instructions when working on vehicles with high-  
voltage system”, page 1 .  
♦ If work near high-voltage system components is necessary,  
perform a visual check of the high-voltage components and  
wires to check for damage ⇒ page 2 .  
♦ If work on high-voltage system components is necessary, de-  
energise high-voltage system ⇒ Rep. gr. 93 ; De-energising  
high-voltage system or ⇒ Electrical system; Rep. gr. 93 ; De-  
energising high-voltage system .  
Note  
The work on the refrigerant circuit using the air conditioner service  
station (here: checking pressure) described in the following can  
only be carried out when the vehicle's drive system is active; if  
necessary, re-energise the high-voltage system.  
– To minimise the number of automatic engine starts when the  
vehicle's drive system is active during test and measurement  
work, charge the vehicle batteries e.g. with the battery  
charger 60A - VAS 5904- in battery standby mode ⇒ Electrical  
system; General information; Rep. gr. 27 ; Battery; Charging  
battery and ⇒ Electrical system; Rep. gr. 93 ; General warning  
instructions 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  
8. Checking pressures  
231  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
parking brake and take care to keep well clear of the engine  
when it is running. Set up any tools needed so that they cannot  
come into contact with moving parts.  
Note  
♦ 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 vehicle's drive  
system does not need to be active.  
♦ The status of the drive system (READY) is shown by the con‐  
trol unit in dash panel insert - J285- via the “power meter” ⇒  
Owner's Manual .  
♦ Activating and deactivating drive system ⇒ Owner's Manual  
(note display of control unit in dash panel insert - J285- ).  
– On vehicles with high-voltage system, switch off (deactivate)  
auxiliary air conditioner function ⇒ Owner's Manual and ⇒  
Infotainment/MMI Operating Manual .  
– Switch off ignition.  
⇒ “7 Connecting air conditioner service station ”, page 187  
⇒ “8 Checking pressures”, page 193  
Note  
If problems are only encountered at one evaporator on vehicles  
fitted with two evaporators (one in air conditioning unit and one in  
battery cooling module or heat exchanger for high-voltage bat‐  
tery), check whether the pressures in the refrigerant circuit are  
OK. Check the pipe connection between the problematic evapo‐  
rator and the outgoing pipe connection at the refrigerant pipe  
distribution point (for cross-sectional restriction or blockage, e.g.  
in restrictor in the refrigerant line to the heat exchanger for high-  
voltage battery). If no fault is found, discharge the refrigerant  
circuit and re-fill it with the specified quantity of refrigerant. Then  
check the pressures and the cooling output of the air conditioner  
again. If the problem persists, check/renew the following compo‐  
nents: if the problem only occurs on the evaporator in the air  
conditioning unit, check/renew the shut-off valve upstream of the  
evaporator (e.g. -N516- or -N541- ). When not activated, this  
component is open and allows the refrigerant to flow through.  
Renew the expansion valve at the evaporator in the air condition‐  
ing unit if no fault is found on -N516- / -N541- . If the problem only  
occurs on the evaporator for cooling the high-voltage components  
(e.g. in the battery cooling module), check the actuation of shut-  
off valve -N517- on the expansion valve on the evaporator in the  
battery cooling module (when not activated, it is closed and does  
not allow the refrigerant to flow through). If the problem only oc‐  
curs on the heat exchanger for high-voltage battery, check the  
shut-off valve -N542- (the valve is open when it is not activated  
and allows refrigerant to flow through) and the restrictor integrated  
in the refrigerant line ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-specific Workshop Manual).  
– Check the pressures in the refrigerant circuit (with the air con‐  
ditioner service station) with the ignition switched off  
⇒ page 195 .  
The pressures with the ignition switched off correspond to the  
specifications.  
– To minimise the number of automatic engine starts when the  
vehicle's drive system is active during test and measurement  
work, charge the vehicle batteries e.g. with the battery  
232  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
charger 60A - VAS 5904- in battery standby mode ⇒ Electrical  
system; General information; Rep. gr. 27 ; Battery; Charging  
battery and ⇒ Electrical system; Rep. gr. 93 ; General warning  
instructions for work on the high-voltage system .  
Note  
♦ 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 vehicle's drive  
system does not need to be active.  
♦ On vehicles with a high-voltage system, the engine does not  
have to be running to check the pressures in the refrigerant  
circuit.  
♦ The status of the drive system (READY) is shown by the con‐  
trol unit in dash panel insert - J285- via the “power meter” ⇒  
Owner's Manual .  
♦ Activating vehicle drive system (check "READY" display in  
control unit in dash panel insert - J285- ) ⇒ Owner's Manual  
– Activate vehicle drive system ⇒ Owner's Manual .  
– Switch on air conditioner.  
– Observe the pressure reading (e.g. pressure gauge) of the air  
conditioner service station.  
Note  
♦ The electrically driven air conditioner compressor is actuated  
by the vehicle electronics. The engine speed has no influence  
on the cooling output of the air conditioner.  
♦ When the vehicle is stationary or only moving slowly (up to a  
speed of approx. 45 km/h), the air conditioner compressor is  
not activated at the maximum specified speed (of approx.  
8500 rpm); the air conditioner compressor speed is limited to  
approx. 5000 rpm.  
♦ Activation of the electrically driven air conditioner compressor  
can be monitored via Guided Fault Finding ⇒ Vehicle diag‐  
nostic tester, “Guided Fault Finding” mode for air conditioner  
and battery regulation .  
♦ Measure the pressures at the service connections; the fitting  
locations of these connections are vehicle-specific ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
8. Checking pressures  
233  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
⇒ “8.6.1 Specifications for pressures in refrigerant circuit on ve‐  
hicles without heat pump”, page 234  
⇒ “8.6.2 Specifications for pressures in refrigerant circuit on ve‐  
hicles with heat pump”, page 254  
8.6.1  
Specifications for pressures in refriger‐  
ant circuit on vehicles without heat pump  
Note  
No non-return valves are installed in the refrigerant circuit on ve‐  
hicles with high-voltage system on which no heat pump is fitted  
(e.g. Audi A3 e-tron, Audi Q5 hybrid, Audi A6 hybrid and Audi A8  
hybrid). On these vehicles, however, valves are installed in the  
refrigerant circuit with regulate the flow of refrigerant to the evap‐  
orator (in the heater and air conditioning unit) or to the heat  
exchanger for cooling high-voltage system components. These  
valves only have 2 operating positions (open or closed) ⇒ Heat‐  
ing, air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-  
specific Workshop Manual) and ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode for air conditioner and battery reg‐  
ulation .  
High-pressure side:  
Increasing from initial pressure (when connecting pressure  
gauges) up to max. 20 bar  
Low-pressure side:  
Dropping from initial pressure (when connecting pressure  
gauges) to a value between 1.5 and 2.3 bar absolute (depending  
on cooling output required)  
Air conditioner compressor speed:  
Between 800 and 8600 rpm depending on cooling output required  
(currently max. 5000 rpm with vehicle stationary)  
234  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ The temperature of the air downstream of the evaporator, the  
current air conditioner compressor speed and the refrigerant  
pressure on the high-pressure side are displayed as meas‐  
ured values by various control units depending on the vehicle  
(e.g. operating and display unit, Climatronic control unit -  
J255- , operating and display unit for front air conditioning  
system - E87- , thermal management control unit - J1024- etc.)  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode for  
air conditioner and ⇒ Current flow diagrams, Electrical fault  
finding and Fitting locations.  
♦ If a very high cooling output is required (e.g. high ambient  
temperature and high fresh air blower speed), the air condi‐  
tioner compressor cannot initially set the pressure on the low-  
pressure side to the necessary value (e.g. for a certain time  
after switching on the air conditioner). When the vehicle is sta‐  
tionary or only moving slowly (up to a speed of approx. 45 km/  
h), the air conditioner compressor is not activated at the max‐  
imum specified speed (of approx. 8500 rpm); the air condi‐  
tioner compressor speed is limited to approx. 5000 rpm.  
Limitation of the maximum permissible air conditioner com‐  
pressor speed is only cancelled at vehicle speeds above  
approx. 45 km/h. At an air conditioner compressor speed of  
5000 rpm, with a high ambient temperature and a high fresh  
air blower speed (unfavourable ambient conditions), the out‐  
put (delivery volume) of the air conditioner compressor is not  
initially sufficient to reduce the pressure on the low-pressure  
side to the specified value. One way of checking the control  
action of the air conditioner compressor under these condi‐  
tions is to actuate 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 using the  
“Guided Fault Finding” function of the air conditioner and the  
battery regulation and ⇒ Heating, air conditioning; Rep. gr.  
00 ; Repair instructions; Checking the cooling output (vehicle-  
specific Workshop Manual).  
♦ Under unfavourable conditions (very high ambient tempera‐  
tures, high humidity), the pressure on the high-pressure side  
may increase to max. 29 bar.  
♦ The specified speed of the air conditioner compressor is dis‐  
played as a measured value by various control units depend‐  
ing on the vehicle (e.g. operating and display unit, Climatronic  
control unit - J255- ) ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode for air conditioning system and ⇒ Current  
flow diagrams, Electrical fault finding and Fitting locations).  
♦ The high pressure measured by the corresponding sender  
(e.g. refrigerant pressure and temperature sender - G395- or  
pressure sender for refrigerant circuit - G805- ) is displayed as  
a measured value by the corresponding control unit (e.g. op‐  
erating and display unit, Climatronic control unit - J255- ) ⇒  
Vehicle diagnostic tester in “Guided Fault Finding” mode for  
air conditioner and ⇒ Heating, air conditioning; Rep. gr. 00 ;  
Repair instructions; Checking cooling output (vehicle-specific  
Workshop Manual).  
♦ Depending on the speed of the air conditioner compressor and  
the control characteristic of the expansion valve, the low pres‐  
sure settles in the tolerance band within the air conditioner  
compressor output range (1.5 to 2.3 bar).  
♦ The specified air conditioner compressor speed must be high‐  
er than 1500 rpm for this test.  
8. Checking pressures  
235  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ In the “maximum cooling output” setting, the specified speed  
is regulated to approx. 4000 to 5000 rpm. This value is vehicle-  
specific and is displayed as a measured value by the corre‐  
sponding control unit (e.g. operating and display unit,  
Climatronic control unit - J255- ) ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode for air conditioner and battery  
regulation .  
♦ On the absolute pressure scale, 0 bar corresponds to an ab‐  
solute vacuum. Normal ambient pressure corresponds to an  
absolute pressure of 1 bar. On the scale 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 using the “Guided Fault Finding” function for the air con‐  
ditioner and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair  
instructions; Checking the cooling output (vehicle-specific  
Workshop Manual).  
♦ On vehicles with two evaporators (e.g. Audi A8 hybrid: one in  
the air conditioning unit and one for cooling the high-voltage  
components e.g. in the battery cooling module / Audi A3 e-  
tron: in the heat exchanger for high-voltage battery), if the  
measured temperature corresponds to or is below the speci‐  
fied value at one evaporator but the required specified value  
is not attained at the other evaporator, the system is controlled  
as follows: the responsible control unit ( -J840- or -J255- ) ac‐  
tivates the electric air conditioner compressor - JX1- at a  
higher speed via various other control units (e.g. power and  
control electronics for electric drive - J842- and control unit for  
air conditioning compressor - V470- ). This causes the cooling  
output of the air conditioner to increase and the pressure on  
the low-pressure side and the evaporator temperature to drop.  
If the required temperature value is then not reached at one  
evaporator, the relevant control unit (e.g. the -J840- or -J255- )  
actuates the integrated shut-off valves ( -N516- , -N541- , -  
N517- or -N542- ) so that refrigerant no longer flows through  
the evaporator which is too cold ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode for air conditioner , ⇒ Current  
flow diagrams, Electrical fault finding and Fitting locations and  
⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking the cooling output (vehicle-specific Workshop Man‐  
ual).  
♦ As the output of the evaporator for cooling the high-voltage  
components (in the battery cooling module and in the high-  
voltage battery heat exchanger) is considerably less than that  
of the evaporator in the air conditioning unit, the required tem‐  
perature may still be reached in the evaporator for cooling the  
high-voltage components when there is insufficient refrigerant  
in the circuit, but the required temperature will no longer be  
reached at the evaporator in the air conditioning unit (although  
the air conditioner compressor is being activated at a higher  
speed).  
236  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure remains con‐ ♦ Actuation of air conditioner compres‐ – Check actuation and opera‐  
stant or only increases  
slightly (above pressure  
with engine stopped)  
sor not OK ⇒ Vehicle diagnostic tester,  
“Guided Fault Finding” function for air  
conditioner, air conditioner compres‐  
sor and battery regulation .  
tion of the air conditioner  
compressor  
– Extract refrigerant from re‐  
frigerant circuit.  
•
•
Low pressure drops quickly  
to specified value or below. ♦ Not enough refrigerant in circuit  
Required cooling output is ♦ Expansion valve for evaporator in air  
•
If quantity of refrigerant ex‐  
tracted is substantially less  
than specified capacity:  
not attained in evaporator in  
air conditioning unit and in  
evaporator for cooling high-  
voltage components.  
conditioning unit defective.  
♦ Shut-off valve upstream of evaporator  
in air conditioning unit (e.g. -N516- or -  
N541- , depending on vehicle) faulty  
(blocked) ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Manual).  
– Locate leak with leak detec‐  
tor and repair it.  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
•
•
High pressure normal  
Low pressure corresponds  
to specified value  
– Shut-off valve upstream of  
evaporator in air conditioning  
unit (e.g. -N516- or -N541- ,  
depending on vehicle) faulty  
(blocked) ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Re‐  
frigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
•
Required cooling output is  
not attained.  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
Observe notes ⇒ page 239 .  
8. Checking pressures  
237  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
Possible causes of fault  
Fault elimination  
fication  
On vehicles without shut-off  
valve upstream of evaporator  
in air conditioning unit (e.g. -  
N516- or -N541- , depending  
on vehicle) ⇒ Heating, air con‐  
ditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific  
Workshop Manual).  
♦ Actuation of air conditioner compres‐ – Extract refrigerant from re‐  
sor not OK ⇒ Vehicle diagnostic tester,  
“Guided Fault Finding” function for air  
conditioner, air conditioner compres‐  
sor and battery regulation .  
frigerant circuit.  
•
If quantity of refrigerant ex‐  
tracted is substantially less  
than specified capacity:  
♦ Not enough refrigerant in circuit  
– Locate leak with leak detec‐  
tor and repair it.  
♦ Expansion valve for evaporator in air  
conditioning unit defective.  
•
•
High pressure normal  
low pressure too low (below  
specified value)  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
Required cooling output is  
not attained at evaporator in  
air conditioning unit.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
– Renew expansion valve for  
evaporator in air conditioning  
unit.  
– Re-charge refrigerant circuit.  
– Repeat test.  
On a vehicle with a shut-off  
valve upstream of the evapo‐  
rator in the air conditioning unit  
(e.g. -N516- or -N541- (de‐  
pending on vehicle) ⇒ Heating,  
air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-  
specific Workshop Manual).  
♦ Actuation of air conditioner compres‐ – Extract refrigerant from re‐  
sor not OK ⇒ Vehicle diagnostic tester,  
“Guided Fault Finding” function for air  
conditioner, air conditioner compres‐  
sor and battery regulation .  
frigerant circuit.  
•
The quantity of refrigerant  
extracted is much less than  
the specified capacity (con‐  
tinue in same way as a vehi‐  
cle without a shut-off valve  
upstream of the evaporator  
in the air conditioning unit)  
♦ Not enough refrigerant in circuit  
♦ Expansion valve for evaporator in air  
conditioning unit defective.  
•
•
High pressure normal  
low pressure too low (below  
specified value)  
♦ Shut-off valve upstream of the evapo‐  
rator in the air conditioning unit (e.g. -  
N516- or -N541- (depending on vehi‐  
cle) defective (closed) ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Workshop  
Manual).  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
•
The required cooling output  
is not attained at the evap‐  
orator in the air conditioning  
unit and at the evaporator  
for cooling the high-voltage  
components.  
– Check activation and opera‐  
tion of shut-off valve up‐  
stream of evaporator in air  
conditioning unit (e.g. -N516-  
or -N541- ) and shut-off valve  
upstream of evaporator for  
cooling high-voltage compo‐  
nents (e.g. -N517- or -  
N542- , depending on vehi‐  
cle) ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
Workshop Manual).  
– Renew expansion valve up‐  
stream of evaporator in air  
conditioning unit.  
– Replace expansion valve (or  
restrictor) upstream of the  
evaporator for cooling the  
high-voltage components.  
– Re-charge refrigerant circuit.  
– Repeat test.  
238  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If no fault is found for this problem, clean refrigerant circuit (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ). Constriction or  
blockage in the refrigerant circuit may also lead to one of these  
problems.  
♦ Depending on vehicle, check measured values of evaporator  
output temperature sender - G263- and, if fitted, of tempera‐  
ture sensor before evaporator for hybrid battery - G756- and  
of temperature sensor after evaporator for hybrid battery -  
G757- as well as activation of air conditioner compressor via  
corresponding control units, e.g. control unit for air condition‐  
ing compressor - J842- by battery regulation control unit -  
J840- or by air conditioner operating and display unit  
( Climatronic control unit - J255- ) ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode for air conditioner and battery  
regulation , ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific Workshop Manual) and ⇒ Cur‐  
rent flow diagrams, Electrical fault finding and Fitting locations.  
♦ Incorrect measured values from -G263- (or e.g. -G756- / -  
G757- ) can also cause problems with the cooling output, or  
the evaporator in the air conditioning unit may ice up ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode for air con‐  
ditioner and battery regulation and ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Workshop  
Manual).  
♦ If, e.g. after renewing the expansion valve, operation of the air  
conditioning system is not OK when the test is repeated (re-fit  
old expansion valve), clean the refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or blow out with compressed air  
and nitrogen ⇒ page 95 ). Then renew the air conditioner com‐  
pressor and receiver/desiccant cartridge.  
♦ If a temperature sensor is faulty, the evaporator may ice up  
although the quantity of refrigerant in the circuit is OK.  
♦ If the expansion valve at the evaporator in the air conditioning  
unit (or e.g. -N516- / -N541- , depending on vehicle) is defec‐  
tive (i.e. is permanently closed or does not open sufficiently),  
the air conditioner compressor is activated to maximum output  
and the low pressure drops to the value in the graph or below  
(air conditioner compressor draws off refrigerant from low-  
pressure side). However, because no refrigerant can flow via  
the expansion valve, the cooling output is not attained and the  
high pressure may also not increase or only increase slightly  
since there is no energy exchange ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode for air conditioner and battery  
regulation , ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific Workshop Manual) and ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific Workshop Manual).  
8. Checking pressures  
239  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ The evaporator in the air conditioning unit has a higher output  
than the evaporator for cooling the high-voltage components  
(e.g. in the battery cooling module or heat exchanger for high-  
voltage battery, depending on vehicle). The shut-off valve (e.g.  
refrigerant shut-off valve 2 for hybrid battery - N517- on the  
expansion valve in the battery cooling module or refrigerant  
shut-off valve for high-voltage battery heat exchanger -  
N542- ) is activated by the battery regulation control unit - A2-  
or air conditioner operating and display unit ( Climatronic  
control unit - AX1- ) when the battery reaches or exceeds a  
certain temperature, depending on the type of cooling used for  
the drive battery - J840- / hybrid battery unit - J255- (hybrid  
battery); energy exchange via the evaporator for cooling the  
high-voltage components (in the battery cooling module or  
heat exchanger for high-voltage battery) is not increased or  
only slightly increased ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode for air conditioner and battery regulation ,  
⇒ 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 .  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
On a vehicle with a shut-off  
valve upstream of the evapo‐  
rator in the air conditioning unit  
(e.g. -N516- or -N541- (de‐  
pending on vehicle) ⇒ Heating,  
air conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-  
specific Workshop Manual).  
♦ Actuation of air conditioner compres‐ – Extract refrigerant from re‐  
sor not OK ⇒ Vehicle diagnostic tester,  
“Guided Fault Finding” function for air  
conditioner, air conditioner compres‐  
sor and battery regulation .  
frigerant circuit.  
•
If the amount of refrigerant  
extracted is significantly less  
than the specified capacity:  
♦ Not enough refrigerant in circuit  
– Locate leak with leak detec‐  
tor and repair it.  
♦ Expansion valve for evaporator in air  
conditioning unit defective.  
•
•
High pressure normal  
low pressure too low (below  
specified value)  
– Re-charge refrigerant circuit.  
– Repeat test.  
♦ Shut-off valve upstream of the evapo‐  
rator in the air conditioning unit (e.g. -  
N516- or -N541- (depending on vehi‐  
cle) defective (closed) ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Workshop  
Manual).  
•
The required cooling output  
is not attained solely at the  
evaporator in the air condi‐  
tioning unit (the cooling out‐  
put is OK at the evaporator  
for cooling the high-voltage  
components).  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
– Check activation and opera‐  
tion of shut-off valve (e.g. -  
N516- or -N541- , depending  
on vehicle); renew expan‐  
sion valve at evaporator in air  
conditioning unit if no fault is  
found ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific  
Workshop Manual).  
– Re-charge refrigerant circuit.  
– Repeat test.  
240  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure normal  
On vehicles with a battery cooling module – Check operation and activa‐  
♦ Actuation or operation of refrigerant  
shut-off valve 2 for hybrid battery -  
N517- , of a control motor, blower or  
temperature sensor in or at battery  
cooling module not OK.  
tion of the components for  
cooling the high-voltage  
components ⇒ Vehicle diag‐  
nostic tester in “Guided Fault  
Finding” mode for air condi‐  
tioner, air conditioner com‐  
pressor and battery regula‐  
tion  
•
low pressure too low (below  
specified value)  
•
The required cooling output  
is not attained solely at the  
evaporator for cooling the  
high-voltage components  
(the cooling output is OK at  
the evaporator in the air  
conditioning unit).  
♦ Constriction or blockage in the refrig‐  
erant line to or from the expansion  
valve at the battery cooling module  
– Check refrigerant lines  
♦ Expansion valve for evaporator for  
cooling high-voltage components de‐  
fective  
– Extract refrigerant from re‐  
frigerant circuit.  
♦ Not enough refrigerant in circuit  
– Depending on vehicle, fit -  
N517- in place of expansion  
valve ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific  
Workshop Manual).  
On vehicles with a heat exchanger for  
high-voltage battery  
– Check restrictor in refriger‐  
ant line to heat exchanger for  
high-voltage battery and  
♦ Activation or operation of shut-off valve  
(e.g. refrigerant shut-off valve for high-  
voltage battery heat exchanger -  
clean or renew, if necessary.  
N542- , faulty refrigerant pump or fault – Re-charge refrigerant circuit.  
in refrigerant circuit for high-voltage  
components ⇒ Heating, air condition‐ – Repeat test.  
ing; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
♦ Constriction or obstruction in the refrig‐  
erant lines leading to or from the heat  
exchanger for high-voltage battery  
♦ Restrictor in the refrigerant line to the  
heat exchanger for high-voltage bat‐  
tery blocked  
♦ Not enough refrigerant in circuit  
8. Checking pressures  
241  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ On vehicles with battery cooling module, the refrigerant shut-  
off valve 2 for hybrid battery - A2- is currently activated by the  
battery regulation control unit - N517- in order to cool the drive  
battery - J840- (hybrid battery) only when the battery reaches  
a certain temperature. If air conditioning mode has not already  
been activated at this point, the electrical air conditioner com‐  
pressor - V470- is actuated via the control unit for air condi‐  
tioning compressor - J842- by -J840- . The temperature of the  
air upstream and downstream of the evaporator in the battery  
cooling module is determined by -J840- . If it is established  
that the cooling is not sufficient, this is stored in -J840- ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode for air  
conditioner, air conditioner compressor and battery regulation  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Workshop Manual).  
♦ On vehicles with a battery cooling module, the temperature of  
the air (and thus the cooling output of the evaporator) in the  
battery cooling module is determined by way of built-in tem‐  
perature sensors (at present it cannot be measured with a  
thermometer during operation) and can only be checked using  
the Guided Fault Finding routine ⇒ Vehicle diagnostic tester,  
“Guided Fault Finding” function for air conditioner, air condi‐  
tioner compressor and battery regulation .  
♦ On vehicles with a battery cooling module, observe additional  
information ⇒ page 239 .  
♦ On some vehicles with a heat exchanger for high-voltage bat‐  
tery (e.g. Audi A3 e-tron; components may have a different  
designation on other vehicles), the refrigerant shut-off valve  
for high-voltage battery heat exchanger - A2- is no longer ac‐  
tivated by the operating unit ( Climatronic control unit - J1050- )  
above a certain temperature in order to cool the high-voltage  
components, e.g. the drive battery - N542- and the high-volt‐  
age battery charger control unit - J255- ( -N542- is open when  
the system is de-energised. If air conditioning mode has not  
already been activated at this point, the operating unit -V470-  
actuates the electrical air conditioner compressor - J842- via  
the control unit for air conditioning compressor - J255- . Other  
components in this circuit must be actuated (e.g. refrigerant  
circulation pump 2 - V178- and solenoid valve 1 - N88- ) and  
the refrigerant must flow through the heat exchanger for high-  
voltage battery to ensure that the refrigerant actually cools the  
high-voltage components. If it is established that the cooling  
of the high-voltage components is not sufficient, this is stored  
in various control units ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode for air conditioner, air conditioner com‐  
pressor and battery regulation , ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Workshop  
Manual) and ⇒ Rep. gr. 19 ; Cooling system/coolant; Con‐  
nection diagram - coolant hoses .  
♦ If no fault is found for this problem, clean refrigerant circuit (by  
flushing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ). Constriction or  
blockage in the refrigerant circuit may also lead to one of these  
problems.  
242  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible devia‐ Possible causes of  
Fault elimination  
tion from specifi‐  
cation  
fault  
On a vehicle with ♦ Air conditioner  
– Check actuation  
and operation of the  
air conditioner com‐  
pressor and repair if  
necessary ⇒ Vehi‐  
cle diagnostic test‐  
er, “Guided Fault  
Finding” function  
for air conditioner  
and battery regula‐  
tion  
a shut-off valve  
upstream of the  
evaporator in the  
air conditioning  
unit (e.g. -N516-  
or -N541- (de‐  
pending on vehi‐  
cle) ⇒ Heating,  
air conditioning;  
Rep. gr. 87 ; Re‐  
frigerant circuit  
(vehicle-specific  
Workshop Man‐  
ual).  
compressor is not  
activated or driv‐  
en.  
♦ Shut-off valve -  
N516- or -N541-  
(depending on  
vehicle) faulty  
(blocked) ⇒  
Heating, air con‐  
ditioning; Rep.  
gr. 87 ; Refriger‐  
ant circuit (vehi‐  
cle-specific  
– Check activation  
and operation of  
shut-off valve (e.g. -  
N516- or -N541- ,  
depending on vehi‐  
cle); renew expan‐  
sion valve at evap‐  
orator in air condi‐  
tioning unit if no  
fault is found ⇒  
Workshop Man‐  
ual).  
•
High pres‐  
sure does not  
rise or only  
rises slightly  
above the  
pressure with  
the engine  
stopped.  
Heating, air condi‐  
tioning; Rep. gr.  
87 ; Refrigerant cir‐  
cuit (vehicle-specif‐  
ic Workshop Man‐  
ual).  
•
•
Low pressure  
does not drop  
or only drops  
slightly.  
Required  
cooling out‐  
put is not at‐  
tained in  
evaporator in  
air condition‐  
ing unit (and  
in evaporator  
for cooling  
high-voltage  
components)  
♦ Constriction or  
blockage in re‐  
frigerant circuit  
(e.g. in refrigerant  
line between  
– Clean refrigerant  
circuit (flush with re‐  
frigerant R134a  
⇒ page 100 or blow  
out with com‐  
service connec‐  
tion on low-pres‐  
sure side and air  
pressed air and ni‐  
trogen ⇒ page 95 ).  
conditioner com‐ – Renew hose or pipe  
pressor).  
if kinked or constric‐  
ted.  
♦ Air conditioner  
compressor de‐  
fective  
– Renew air condi‐  
tioner compressor.  
8. Checking pressures  
243  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
On a vehicle without a shut-off ♦ Activation or operation of air con‐ – Check actuation and operation of the  
valve upstream of the evapo‐  
rator in the air conditioning  
unit (e.g. -N516- or -N541-  
(depending on vehicle) ⇒  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
ditioner compressor not OK  
air conditioner compressor and re‐  
pair if necessary ⇒ Vehicle diagnos‐  
tic tester, “Guided Fault Finding”  
function for air conditioner and bat‐  
tery regulation  
♦ Constriction or blockage in refrig‐  
erant circuit  
♦ Expansion valve defective  
– Run hand over refrigerant circuit to  
check for differences in temperature.  
•
•
•
High pressure increases  
above specification  
•
If there is a difference in temperature  
at one component:  
Low pressure drops quick‐  
ly to specified value  
– Renew hose or pipe if kinked or con‐  
stricted.  
Required cooling output is  
not attained in evaporator  
in air conditioning unit (and  
in evaporator for cooling  
high-voltage components)  
– In the event of clogging, clean refrig‐  
erant circuit (flush with refrigerant  
R134a ⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
If operation is not OK and no fault is  
found:  
– Clean refrigerant circuit (flush with  
refrigerant R134a ⇒ page 100 or  
blow out with compressed air and ni‐  
trogen ⇒ page 95 ).  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not OK:  
– Renew expansion valve upstream of  
evaporator in air conditioning unit  
and receiver.  
On a vehicle with a shut-off ♦ Activation or operation of air con‐ – Check activation and operation of air  
valve upstream of the evapo‐  
rator in the air conditioning  
unit (e.g. -N516- or -N541-  
(depending on vehicle) ⇒  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
ditioner compressor or shut-off  
valve (e.g. -N516- or -N541- , de‐  
pending on vehicle) faulty. ⇒  
Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Manual).  
conditioner compressor and shut-off  
valves (e.g. -N516- ) ⇒ Vehicle di‐  
agnostic tester in “Guided Fault  
Finding” mode for air conditioner and  
battery regulation and ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refriger‐  
ant circuit (vehicle-specific Work‐  
shop Manual).  
♦ Constriction or blockage in refrig‐  
erant circuit  
•
•
•
High pressure increases  
above specification  
– Perform further testing as described  
for vehicles without shut-off valve  
upstream of evaporator.  
♦ Expansion valve defective  
low pressure quickly drops  
to specified value,  
Required cooling output is  
not attained in evaporator  
in air conditioning unit (and  
in evaporator for cooling  
high-voltage components)  
244  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If the operation of the air conditioner is not OK when the test  
is repeated, renew the expansion valve and receiver (and -  
N516- / -N541- if fitted) ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific Workshop Manual).  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ If the expansion valve at the evaporator in the air conditioning  
unit or the shut-off valve (e.g. -N516- or -N541- ) is defective  
(is permanently closed or does not open sufficiently), the air  
conditioner compressor is activated to maximum output and  
the low pressure drops to the specified value or below (air  
conditioner compressor draws off refrigerant from low-pres‐  
sure side). However, because no refrigerant (or only a small  
amount) can flow via the expansion valve (the corresponding  
shut-off valve), the cooling output is not attained and the high  
pressure may also not increase or only increase slightly since  
there is no energy exchange ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode for air conditioner and battery  
regulation , ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific Workshop Manual) and ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific Workshop Manual).  
♦ If a vehicle has a battery cooling module and the expansion  
valve on the evaporator in the battery cooling module is de‐  
fective (or refrigerant shut-off valve 2 for hybrid battery - N517-  
is not operating or is not actuated properly), or if the expansion  
valve is permanently closed or does not open sufficiently, the  
air conditioner compressor is also actuated to maximum out‐  
put (the required temperatures in the battery cooling module  
are not reached). The pressure on the low-pressure side then  
only drops to or below the specified value if no cooling output  
is requested in the air conditioning unit at the same time (the  
shut-off valve upstream of the evaporator in the air condition‐  
ing unit, e.g. -N516- , is activated and closed). The air condi‐  
tioner compressor draws off the refrigerant from the low-  
pressure side of both evaporators. However, as no refrigerant  
can flow via the expansion valve in the air conditioning unit  
(e.g. -N516- ) and the cooling output is not reached in the bat‐  
tery cooling module (fault in area of battery cooling module),  
the electric air conditioner compressor is activated at a higher  
speed. However, as no more refrigerant can flow, the pressure  
on the low-pressure side drops below the specified value and  
the high pressure may also not increase or only increase  
slightly since there is no energy exchange ⇒ Vehicle diag‐  
nostic tester in “Guided Fault Finding” mode for air conditioner  
and battery regulation , ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific Workshop Manual)  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific Workshop  
Manual).  
8. Checking pressures  
245  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ On vehicles with a high-voltage battery heat exchanger, if the  
restrictor installed in the refrigerant line to the high-voltage  
battery heat exchanger is blocked or the shut-off valve (e.g.  
refrigerant shut-off valve for high-voltage battery heat ex‐  
changer - N542- on the Audi A3 e-tron) installed in this line is  
faulty, permanently closed or does not open far enough, the  
air conditioner compressor is also activated to maximum out‐  
put (the required temperatures in the refrigerant circuit are not  
reached with the high-voltage battery heat exchanger). The  
pressure on the low-pressure side then only drops to or below  
the specified value if no cooling output is requested in the air  
conditioning unit at the same time ( -N541- is activated and  
closed, e.g. on the Audi A3 e-tron). The air conditioner com‐  
pressor draws off the refrigerant from the low-pressure side of  
both evaporators. However, because refrigerant cannot flow  
via the expansion valve into the air conditioning unit (via the  
shut-off valve, e.g. -N541- ) and the cooling output in the high-  
voltage battery heat exchanger is not reached, the electric air  
conditioner compressor is activated at a higher speed. How‐  
ever, as no more refrigerant can flow, the pressure on the low-  
pressure side drops below the specified value and the high  
pressure may also not increase or only increase slightly since  
there is no energy exchange ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode for air conditioner and battery  
regulation , ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐  
erant circuit (vehicle-specific Workshop Manual) and ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific Workshop Manual).  
The same applies if a fault occurs in the coolant circuit where  
the high-voltage battery heat exchanger is installed (e.g. cool‐  
ant circulation pump 2 - V178- or solenoid valve 1 - N88- (on  
Audi A3 e-tron) are not activated correctly or are faulty). Al‐  
though the high-voltage battery heat exchanger is cooled, the  
coolant does not reach the high-voltage components which  
need to be cooled ⇒ Heating, air conditioning; Rep. gr. 87 ;  
Coolant circuit (vehicle-specific Workshop Manual) and ⇒  
Rep. gr. 19 ; Cooling system/coolant; Connection diagram -  
coolant hoses .  
♦ As the cooling output of the evaporator for cooling the high-  
voltage battery is less than that of the evaporator in the air  
conditioning unit, the required temperature in the evaporator  
for cooling the high-voltage battery may still be reached when  
there is not enough refrigerant in the circuit, but the required  
temperature will no longer be reached at the evaporator in the  
air conditioning unit (although the air conditioner compressor  
is activated at a higher speed).  
♦ If there is too much refrigerant oil in the circuit, also discharge  
(flush) the air conditioner compressor and renew the receiver/  
desiccant cartridge. After cleaning the refrigerant circuit (flush‐  
ing with refrigerant R134a ⇒ page 100 or blowing out with  
compressed air and nitrogen ⇒ page 95 ), add the correct  
amount of refrigerant oil to the circuit (to the air conditioner  
compressor) ⇒ page 333 .  
246  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
•
•
•
High and low pressure nor‐ ♦ Activation or operation of air condition‐ – Check activation of air con‐  
mal at first, but after a while:  
er compressor or shut-off valve (e.g. -  
N516- or -N541- , depending on vehi‐  
cle) faulty ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Manual).  
ditioner compressor and  
shut-off valve (e.g. -N516- or  
-N541- ) ⇒ Vehicle diagnos‐  
tic tester in “Guided Fault  
Finding” mode for air condi‐  
tioner and battery regula‐  
tion .  
High pressure rises above  
specified value  
Low pressure drops to  
specified value or below  
♦ Moisture in refrigerant circuit  
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and in  
evaporator for cooling high-  
voltage components)  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Renew receiver with dryer.  
•
•
High and low pressure nor‐  
mal at first  
– Evacuate refrigerant circuit  
for at least 3 hours.  
After driving for a while, low  
pressure drops below  
specified value (evaporator  
in air conditioning unit ices  
up)  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
♦ It is not initially necessary to clean the refrigerant circuit (flush  
with refrigerant R134a ⇒ page 100 or blow out with com‐  
pressed air and nitrogen ⇒ page 95 ) when this problem  
occurs. Normally, there is only a small quantity of moisture in  
the system which can be removed by lengthy evacuation.  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer in the receiver (adjust quantity  
of refrigerant oil). Subsequently, evacuate refrigerant circuit  
for at least 3 hours.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ A faulty evaporator output temperature sender - G263- and/  
or, if fitted, temperature sensor after evaporator for hybrid bat‐  
tery - G757- (depending on vehicle) may also cause the re‐  
frigerant circuit to ice up. If this problem occurs, also observe  
the measured value for -G263- and -G757- (e.g. on vehicles  
with a battery cooling module) ⇒ Vehicle diagnostic tester; in  
“Guided Fault Finding” mode for air conditioner, ⇒ Heating,  
air conditioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual) and ⇒ Heating, air conditioning; Rep.  
gr. 00 ; Repair instructions; Checking cooling output (vehicle-  
specific Workshop Manual).  
8. Checking pressures  
247  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
Possible causes of fault  
Fault elimination  
fication  
•
•
•
High pressure normal  
Low pressure too low  
♦ Activation or operation of air condition‐ – Check activation and opera‐  
er compressor or, if fitted, shut-off  
valves (e.g. -N516- , -N517- , -N541- or  
-N542- , depending on vehicle) faulty  
⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
tion of air conditioner com‐  
pressor and, if fitted, shut-off  
valves (e.g. -N516- and -  
N517- ) ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode for air conditioner  
and battery regulation and ⇒  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and in  
evaporator for cooling high-  
voltage components)  
♦ Expansion valve in air conditioning unit  
or, if fitted, in battery cooling module  
defective.  
♦ Expansion valve in the air conditioning  
unit faulty or restrictor in the refrigerant  
line to the heat exchanger for high-volt‐  
age battery blocked (if available).  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ) (not always nec‐  
essary, refer to notes).  
♦ Air conditioner compressor defective  
– Renew expansion valve for  
evaporator in air conditioning  
unit and for receiver/dryer.  
– If fitted, renew expansion  
valve for evaporator in bat‐  
tery cooling module or clean/  
renew refrigerant line with re‐  
strictor to the heat exchanger  
for high-voltage battery.  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
– Renew air conditioner com‐  
pressor.  
– Re-charge refrigerant circuit.  
– Repeat test.  
248  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If the fault “High pressure normal, low pressure too low” oc‐  
curs, please note that the evaporator in the air conditioning  
unit may ice up although the amount of refrigerant 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 air conditioner compressor regulating valve - J842- ),  
the refrigerant circuit does not have to be cleaned (by flushing  
with refrigerant R134a ⇒ page 100 or blowing out with com‐  
pressed air and nitrogen ⇒ page 95 ). In this case it is sufficient  
to renew the air conditioner compressor (observe quantity of  
refrigerant oil in compressor and adjust if necessary).  
♦ On vehicles with a battery cooling module, if the expansion  
valve for the evaporator in the air conditioning unit or the ex‐  
pansion valve for the evaporator in the battery cooling module  
is defective (permanently closed or does not open sufficiently),  
the air conditioner compressor is also actuated to maximum  
output and the pressure on the low-pressure side drops to the  
value in the graph or below (the air conditioner compressor  
draws off refrigerant from the low-pressure side). As refriger‐  
ant cannot however flow via the defective expansion valve, the  
cooling output is not attained in the downstream evaporator  
and the high pressure may either not increase or only increase  
slightly due to the absence of energy conversion. However,  
the air conditioner compressor may be activated at a higher  
speed, as the required cooling output is not attained in one  
evaporator. This also applies if operation or activation of a  
shut-off valve (e.g. refrigerant shut-off valve 1 for hybrid bat‐  
tery - N516- or refrigerant shut-off valve 2 for hybrid battery -  
N517- , depending on vehicle) is not OK ⇒ Vehicle diagnostic  
tester; in “Guided Fault Finding” mode for air conditioner, ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual) and ⇒ Heating, air condi‐  
tioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific Workshop Manual).  
♦ On vehicles with a high-voltage battery heat exchanger, if the  
expansion valve for the evaporator in the air conditioning unit  
is defective (permanently closed or does not open far enough)  
or the restrictor in the refrigerant line to the high-voltage bat‐  
tery heat exchanger is blocked, the air conditioner compressor  
is also activated to maximum output and the pressure on the  
low-pressure side drops to the value in the graph or below (the  
air conditioner compressor draws off refrigerant from the low-  
pressure side). However, as refrigerant cannot flow via the  
defective expansion valve or blocked restrictor, the cooling  
output is not attained in the downstream evaporator and the  
high pressure may either not increase or only increase slightly  
since there is no energy exchange. However, the air condi‐  
tioner compressor may be activated at a higher speed, as the  
required cooling output is not attained in one evaporator. This  
also applies if operation or activation of a shut-off valve (e.g.  
refrigerant shut-off valve for heater and air conditioner unit -  
N541- or refrigerant shut-off valve for high-voltage battery heat  
exchanger - N542- , depending on vehicle) or a component  
installed in the refrigerant circuit for high-voltage components  
(e.g. coolant circulation pump 2 - V178- or solenoid valve 1 -  
N88- on Audi A3 e-tron, depending on vehicle) is not OK  
⇒ Vehicle diagnostic tester; in “Guided Fault Finding” mode for  
air conditioner, ⇒ Rep. gr. 19 ; Cooling system/coolant; Con‐  
nection diagram - coolant hoses and ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific  
Workshop Manual).  
8. Checking pressures  
249  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ Check the measured values for the evaporator output tem‐  
perature sender - G263- (and if applicable the measured  
values for the temperature sensor before evaporator for hybrid  
battery - G756- and temperature sensor after evaporator for  
hybrid battery - G757- , depending on vehicle) as well as ac‐  
tivation of the air conditioner compressor by the battery regu‐  
lation control unit - J840- , the air conditioner operating unit  
( Climatronic control unit - J255- ) / operating and display unit  
for front air conditioning system - E87- or thermal management  
control unit - J1024- (depending on vehicle). If the measured  
value of -G263- (or -G756- / -G757- , depending on vehicle)  
or activation of the air conditioner compressor is not OK, the  
evaporator may ice up or the required cooling output is not  
attained ⇒ Vehicle diagnostic tester; in “Guided Fault Finding”  
mode for air conditioner, ⇒ Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-specific Workshop Manual)  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific Workshop  
Manual).  
250  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure normal or too ♦ Activation or operation of air condition‐ – Check activation and opera‐  
high  
er compressor not OK  
tion of air conditioner com‐  
pressor and, if fitted, these  
shut-off valves ( -N516- , -  
N517- , -N541- and -N542- ,  
depending on vehicle) ⇒ Ve‐  
hicle diagnostic tester in  
“Guided Fault Finding” mode  
for air conditioner and bat‐  
tery regulation and ⇒ Heat‐  
ing, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Man‐  
ual).  
•
•
Low pressure too high  
♦ Depending on refrigerant circuit ver‐  
sion, activation or operation of one of  
these shut-off valves ( -N516- , -N517- ,  
-N541- or -N542- , depending on vehi‐  
cle) is not OK ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
Noise from air conditioner  
compressor (particularly af‐  
ter being switched on)  
•
The required cooling output  
is not attained in the evap‐  
orator in the air conditioning  
unit and / or in the evapora‐  
♦ Too much refrigerant in circuit  
tor for cooling the high-volt‐ ♦ Expansion valve defective  
age components.  
♦ Air conditioner compressor defective  
– Extract refrigerant from re‐  
frigerant circuit.  
•
The quantity of refrigerant  
extracted corresponds  
roughly to the actual capaci‐  
ty.  
– Renew expansion valve for  
evaporator in air conditioning  
unit and for receiver/dryer.  
– Renew expansion valve with  
-N517- .  
– Check restrictor in refriger‐  
ant line to heat exchanger for  
high-voltage battery and  
clean or renew, if necessary.  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK.  
– Renew air conditioner com‐  
pressor.  
•
If quantity of refrigerant ex‐  
tracted is significantly great‐  
er than specified capacity:  
– Re-charge refrigerant circuit.  
– Repeat test.  
8. Checking pressures  
251  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ This fault may also be caused by too much refrigerant oil in  
the circuit. Overfilling with refrigerant oil may occur if, for ex‐  
ample, the air conditioner compressor has been renewed  
without adjusting the quantity of refrigerant oil.  
♦ On vehicles with a battery cooling module, if the expansion  
valve for the evaporator in the air conditioning unit or the ex‐  
pansion valve for the evaporator in the battery cooling module  
is defective (permanently closed or does not open sufficiently),  
the air conditioner compressor is also actuated to maximum  
output and the pressure on the low-pressure side drops to the  
value in the graph or below (the air conditioner compressor  
draws off refrigerant from the low-pressure side). As refriger‐  
ant cannot however flow via the defective expansion valve, the  
cooling output is not attained in the downstream evaporator  
and the high pressure may either not increase or only increase  
slightly due to the absence of energy conversion. However,  
the air conditioner compressor may be activated at a higher  
speed, as the required cooling output is not attained in one  
evaporator. This also applies if operation or activation of a  
shut-off valve (e.g. refrigerant shut-off valve 1 for hybrid bat‐  
tery - N516- or refrigerant shut-off valve 2 for hybrid battery -  
N517- , depending on vehicle) is not OK ⇒ Vehicle diagnostic  
tester; in “Guided Fault Finding” mode for air conditioner and  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
♦ On vehicles with a high-voltage battery heat exchanger, if the  
expansion valve for the evaporator in the air conditioning unit  
is defective (permanently closed or does not open far enough)  
or the restrictor in the refrigerant line to the high-voltage bat‐  
tery heat exchanger is blocked, the air conditioner compressor  
is also activated to maximum output and the pressure on the  
low-pressure side drops to the value in the graph or below (the  
air conditioner compressor draws off refrigerant from the low-  
pressure side). However, as refrigerant cannot flow via the  
defective expansion valve or blocked restrictor, the cooling  
output is not attained in the downstream evaporator and the  
high pressure may either not increase or only increase slightly  
since there is no energy exchange. However, the air condi‐  
tioner compressor may be activated at a higher speed, as the  
required cooling output is not attained in one evaporator. This  
also applies if operation or activation of refrigerant shut-off  
valve for heater and air conditioner unit - N541- , refrigerant  
shut-off valve for high-voltage battery heat exchanger - N542-  
(e.g. on Audi A3 e-tron) or a component installed in the refrig‐  
erant circuit for high-voltage components (e.g. coolant circu‐  
lation pump 2 - V178- or solenoid valve 1 - N88- on Audi A3  
e-tron) is not OK ⇒ Vehicle diagnostic tester; in “Guided Fault  
Finding” mode for air conditioner, ⇒ Rep. gr. 19 ; Cooling  
system/coolant; Connection diagram - coolant hoses and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
252  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High and low pressure nor‐ ♦ Activation or operation of air condition‐ – Check activation and opera‐  
mal  
er compressor not OK  
tion of air conditioner com‐  
pressor and, if fitted, these  
shut-off valves (e.g. -N516- ,  
-N517- , -N541- and -N542- )  
⇒ Vehicle diagnostic tester  
in “Guided Fault Finding”  
mode for air conditioner and  
battery regulation and ⇒  
Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant cir‐  
cuit (vehicle-specific Work‐  
shop Manual).  
•
Required cooling output is ♦ Depending on refrigerant circuit ver‐  
not attained in evaporator in  
air conditioning unit (and in  
evaporator for cooling high-  
voltage components)  
sion, activation or operation of one of  
these shut-off valves (e.g. -N516- , -  
N517- , -N541- or -N542- , depending  
on vehicle) is not OK ⇒ Heating, air  
conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Workshop  
Manual).  
♦ Too much refrigerant in circuit  
♦ Expansion valve defective  
– Discharge refrigerant circuit.  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 or blow out with  
compressed air and nitrogen  
⇒ page 95 ).  
– Add correct quantity of refrig‐  
erant oil to circuit (refer to  
note).  
•
•
High and low pressure nor‐  
mal  
Noise from air conditioner  
compressor (particularly af‐  
ter being switched on)  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
•
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and/or  
in evaporator for cooling  
high-voltage components)  
– Renew expansion valve.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If for example the expansion valve for the evaporator in the air  
conditioning unit is defective (permanently open), the evapo‐  
rator temperature (in the air conditioning unit) is no longer  
regulated such that only refrigerant in gas form exits from the  
evaporator. Under certain usage conditions, liquid droplets  
may then be drawn in by the air conditioner compressor and  
result in noise (liquid cannot be compressed).  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flushing with refrigerant R134a  
⇒ page 100 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
8. Checking pressures  
253  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
8.6.2  
Specifications for pressures in refriger‐  
ant circuit on vehicles with heat pump  
Note  
♦ On vehicles with high-voltage system and heat pump (e.g.  
Audi Q7 e-tron), non-return valves and electrically activated  
valves are installed in the refrigerant circuit which regulate the  
flow of refrigerant in the refrigerant circuit depending on the  
current operating mode. There are different versions of these  
valves ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific Workshop Manual) and ⇒ Vehicle di‐  
agnostic tester in “Guided Fault Finding” mode.  
♦ On vehicles with the “heat pump” and/or “high-voltage battery  
cooling” function, high pressure is not available at the service  
connection on the high-pressure side in all air conditioner op‐  
erating modes. On these vehicles, the pressure in the refrig‐  
erant circuit on the high-pressure side can only be measured  
via the pressure/temperature senders installed in the refriger‐  
ant circuit (depending on the air conditioner operating mode)  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual) and ⇒ Vehicle diagnostic  
tester (“Guided Fault Finding”).  
♦ On these vehicles, the air conditioning system's refrigerant  
circuit is used not only to cool the passenger compartment but  
also to cool the hybrid battery unit - AX1- (via the high-voltage  
system's coolant circuit) and heat the passenger compartment  
via the heat pump function when ambient temperatures are  
low. To operate these functions, various valves, pressure/  
temperature senders and pumps in the refrigerant circuit and  
the high-voltage system's coolant circuit must be correctly in‐  
stalled and working properly ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐  
ual), ⇒ Vehicle diagnostic tester in “Guided Fault Finding”  
mode and ⇒ Engine, mechanics; Rep. gr. 19 ; Cooling sys‐  
tem/coolant; Draining and filling cooling system .  
♦ To locate the possible cause of a malfunction, various routines  
have been stored in the basic setting of -J1024- ; these rou‐  
tines activate the “Air conditioner cooling”, “Heat pump” and  
“Cooling of high-voltage system components” functions ⇒ Ve‐  
hicle diagnostic tester (“Guided Fault Finding”).  
High-pressure side:  
Increasing from initial pressure (when connecting pressure  
gauges) up to max. 20 bar  
Note  
Depending on the layout of the service connection (high-pressure  
side) and on the operating mode, it may only be possible to meas‐  
ure the high pressure via the pressure/temperature senders in‐  
stalled in the refrigerant circuit ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Manual).  
Low-pressure side:  
Dropping from initial pressure (when connecting pressure  
gauges) to a value between 1.5 and 2.3 bar absolute (depending  
on cooling output required)  
254  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Air conditioner compressor speed:  
Between 800 and 8600 rpm depending on cooling output required  
(currently max. 5000 rpm with vehicle stationary)  
8. Checking pressures  
255  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ The temperature of the air downstream of the evaporator, the  
current air conditioner compressor speed and the refrigerant  
pressure on the high-pressure side are displayed as meas‐  
ured values by various control units depending on the vehicle  
(e.g. by the thermal management control unit - J1024- , oper‐  
ating and display unit for front air conditioning system - E87-  
or Climatronic control unit - J255- ) ⇒ Heating, air conditioning;  
Rep. gr. 87 ; Refrigerant circuit (vehicle-specific Workshop  
Manual), and ⇒ Vehicle diagnostic tester in “Guided Fault  
Finding” mode.  
♦ If a very high cooling output is required (e.g. high ambient  
temperature and high fresh air blower speed), the air condi‐  
tioner compressor cannot initially set the pressure on the low-  
pressure side to the necessary value (e.g. for a certain time  
after switching on the air conditioner). When the vehicle is sta‐  
tionary or only moving slowly (up to a speed of approx. 45 km/  
h), the air conditioner compressor is not activated at the max‐  
imum specified speed (of approx. 8500 rpm); the air condi‐  
tioner compressor speed is limited to approx. 5000 rpm.  
Limitation of the maximum permissible air conditioner com‐  
pressor speed is only cancelled at vehicle speeds above  
approx. 45 km/h. At an air conditioner compressor speed of  
5000 rpm, with a high ambient temperature and a high fresh  
air blower speed (unfavourable ambient conditions), the out‐  
put (delivery volume) of the air conditioner compressor is not  
initially sufficient to reduce the pressure on the low-pressure  
side to the specified value. One way of checking the control  
action of the air conditioner compressor under these condi‐  
tions is to activate 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 for air conditioner and battery regulation,  
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 humidity), the pressure on the high-pressure side  
may increase to max. 29 bar.  
♦ The specified speed of the air conditioner compressor is dis‐  
played as a measured value e.g. by thermal management  
control unit - J1024- ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode.  
♦ The pressure (low or high pressure) in the refrigerant circuit,  
as measured by the various pressure/temperature senders  
depending on the corresponding operating mode, is displayed  
as a measured value by the corresponding control unit ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
♦ Depending on the air conditioner compressor speed and the  
characteristic curve of the expansion valve (on the evaporator  
for the front heater and air conditioning unit), the low pressure  
settles within the air conditioner compressor output range in  
the tolerance band (1.5 to 2.3 bar).  
♦ The specified air conditioner compressor speed must be high‐  
er than 1500 rpm for this test.  
♦ In the “maximum cooling output” setting, the specified speed  
is regulated to approx. 4000 to 5000 rpm. This value is vehicle-  
specific and is displayed as a measured value by the corre‐  
sponding control unit ⇒ Vehicle diagnostic tester in “Guided  
Fault Finding” mode.  
256  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ On the absolute pressure scale, 0 bar corresponds to an ab‐  
solute vacuum. Normal ambient pressure corresponds to an  
absolute pressure of 1 bar. On the scales of most pressure  
gauges, 0 bar corresponds to an absolute pressure of one bar  
(can be seen from -1 mark below 0).  
♦ On vehicles with 2 evaporators (one in the heater and air con‐  
ditioning unit and one for cooling the high-voltage compo‐  
nents, e.g. the high-voltage battery heat exchanger) and 2  
condensers (one on the front end for the air conditioner and  
one as a heat exchanger for the heat pump function): If the  
measured temperatures or pressures correspond to the spec‐  
ifications for one component but not for another component  
(depending on the selected function), check the activation of  
the electrically activated valves installed in the refrigerant cir‐  
cuit. Also observe the pressure distribution in the refrigerant  
circuit (depending on the non-return valves installed) ⇒ Vehi‐  
cle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
♦ For correct operation of the air conditioner, it is also necessary  
for sufficient heat to be supplied to or discharged from the cor‐  
responding heat exchangers (depending on the selected func‐  
tion). You should therefore also pay attention to the incorpo‐  
ration of the heat exchanger into the corresponding coolant  
circuits for the engine and for the high-voltage system, and to  
the operation of the pumps and valves installed in these ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit (ve‐  
hicle-specific Workshop Manual).  
♦ As the output of the evaporator for cooling the high-voltage  
components (in the battery cooling module and in the high-  
voltage battery heat exchanger) is less than that of the evap‐  
orator in the heater and air conditioning unit, the required  
temperature may still be reached in the evaporator for cooling  
the high-voltage components when there is insufficient refrig‐  
erant in the circuit, but the required temperature will no longer  
be reached at the evaporator in the heater and air conditioning  
unit (although the air conditioner compressor is being activa‐  
ted at a higher speed).  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure remains con‐ ♦ Not enough refrigerant in circuit  
stant or only increases  
– Extract refrigerant from re‐  
frigerant circuit.  
slightly (above pressure  
with engine stopped)  
•
If quantity of refrigerant ex‐  
tracted is substantially less  
than specified capacity:  
•
•
Low pressure drops quickly  
to specified value or below.  
– Locate leak with leak detec‐  
tor and repair it.  
Required cooling output is  
not attained in evaporator in  
air conditioning unit and in  
evaporator for cooling high-  
voltage components.  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
– Check activation and opera‐  
tion of air conditioner com‐  
pressor and of valves instal‐  
led in refrigerant circuit (see  
below).  
8. Checking pressures  
257  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
Possible causes of fault  
Fault elimination  
fication  
♦ Activation of air conditioner compres‐ – Check activation and opera‐  
sor not OK  
tion of air conditioner com‐  
pressor ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode  
•
•
High pressure normal  
♦ One of the valves installed in the re‐ – Check operation and activa‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
tion of the various valves in‐  
stalled in refrigerant circuit  
by observing pressure distri‐  
bution in refrigerant circuit  
⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
Low pressure corresponds  
to specified value  
•
Required cooling output is  
not attained.  
Workshop Manual).  
♦ Not enough refrigerant in circuit  
– Discharge and refill refriger‐  
ant circuit (see above).  
♦ Shut-off valve upstream of expansion  
valve for evaporator in front heater and  
air conditioning unit defective  
– Repeat test.  
– Check shut-off valve ⇒ Heat‐  
ing, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Man‐  
ual).  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
– Renew expansion valve.  
258  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ To locate the possible cause of a malfunction, various routines  
have been stored in the basic setting of the corresponding  
control unit (e.g. -J1024- ); these routines activate the “Air  
conditioner cooling”, “Heat pump” and “Cooling of high-voltage  
system components” functions ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode.  
♦ If no fault is detected for this issue, first check the activation of  
the electrically activated valves installed in the refrigerant cir‐  
cuit. If no fault can be detected, remove and check the non-  
return valves installed in the refrigerant circuit; if it is still not  
possible to detect a fault, clean the refrigerant circuit (with re‐  
frigerant R134a); the issue may alternatively have been  
caused by a constriction or blockage in the refrigerant circuit  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual) and ⇒ page 100 .  
♦ On vehicles with the “heat pump” and/or “high-voltage battery  
cooling” function, high pressure is not available at the service  
connection on the high-pressure side in all air conditioner op‐  
erating modes. On these vehicles, the pressure in the refrig‐  
erant circuit on the high-pressure side can only be measured  
via the pressure/temperature senders installed in the refriger‐  
ant circuit (depending on the air conditioner operating mode)  
⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual) and ⇒ Vehicle diagnostic  
tester (“Guided Fault Finding”).  
♦ Before starting repair work, also check the measured values  
of the various pressure/temperature senders installed in the  
refrigerant circuit. An incorrect measured value from a pres‐  
sure/temperature sender can also cause problems with the  
cooling output, or the evaporator in the front heater and air  
conditioning unit may ice up ⇒ Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehicle-specific Workshop Man‐  
ual), ⇒ 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 high-volt‐  
age battery cooling), also observe the activation and operation  
of the coolant circuit components associated with these func‐  
tions ⇒ Heating, air conditioning; Rep. gr. 87 ; Coolant circuit  
(vehicle-specific Workshop Manual).  
♦ If the test is repeated and operation of the air conditioner is not  
OK, e.g. after renewing the expansion valve (re-fit old expan‐  
sion valve), clean the refrigerant circuit (flush with refrigerant  
R134a ⇒ page 100 ). Then renew the air conditioner com‐  
pressor and receiver/desiccant cartridge.  
♦ If a temperature sensor is faulty, the evaporator may ice up  
although the quantity of refrigerant in the circuit is OK.  
♦ If the expansion valve at the evaporator in the heater and air  
conditioning unit is defective (is permanently closed or does  
not open far enough), the air conditioner compressor is acti‐  
vated to maximum output and the low pressure drops to the  
value in the graph or below (air conditioner compressor draws  
off refrigerant from low-pressure side). However, as refrigerant  
cannot flow via the expansion valve, the cooling output is not  
attained and the high pressure may also not increase or only  
increase slightly since there is no energy exchange ⇒ Vehicle  
diagnostic tester in “Guided Fault Finding” mode and ⇒ Heat‐  
ing, air conditioning; Rep. gr. 00 ; Repair instructions; Check‐  
ing cooling output (vehicle-specific Workshop Manual).  
8. Checking pressures  
259  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
♦ The evaporator in the heater and air conditioning unit has a  
higher output than the evaporator for cooling the high-voltage  
components. Depending on the version, the expansion valve  
upstream of this evaporator (the heat exchanger for cooling  
the high-voltage system components) is currently activated by  
the corresponding control unit in order to cool the drive battery  
- A2- / hybrid battery unit - AX1- (hybrid battery) only above/  
below a certain battery temperature, which means that energy  
exchange via this evaporator does not rise or only rises slightly  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific Workshop  
Manual).  
♦ If there is too much refrigerant oil in the circuit, also discharge  
(flush) the air conditioner compressor and renew the receiver/  
desiccant cartridge. After cleaning the refrigerant circuit (flush‐  
ing with refrigerant R134a ⇒ page 100 ), add the correct  
amount of refrigerant oil to the circuit (to the air conditioner  
compressor) ⇒ page 333 .  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure normal  
♦ Not enough refrigerant in circuit  
– Extract refrigerant from re‐  
frigerant circuit.  
•
Low pressure normal or too  
low (below specified value)  
•
If the amount of refrigerant  
extracted is significantly less  
than the specified capacity:  
•
The required cooling output  
is not attained solely at the  
evaporator in the air condi‐  
tioning unit (the cooling out‐  
put is OK at the evaporator  
for cooling the high-voltage  
components).  
– Locate leak with leak detec‐  
tor and repair it.  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
If amount of refrigerant ex‐  
tracted roughly corresponds  
to specified capacity:  
– Check activation and opera‐  
tion of air conditioner com‐  
pressor and of valves instal‐  
led in refrigerant circuit (see  
below).  
♦ Activation of air conditioner compres‐ – Check activation and opera‐  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
♦ One of the valves installed in the re‐ – Check operation and activa‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
tion of the various valves in‐  
stalled in refrigerant circuit  
by observing pressure distri‐  
bution in refrigerant circuit  
⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
Workshop Manual).  
260  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
♦ Shut-off valve upstream of expansion – Check shut-off valve ⇒ Heat‐  
valve for evaporator in front heater and  
air conditioning unit defective  
ing, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Man‐  
ual).  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
– Renew expansion valve  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
Observe notes ⇒ page 259 .  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
•
High pressure normal  
♦ One of the valves installed in the re‐ – Check operation and activa‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
tion of the various valves in‐  
stalled in refrigerant circuit  
by observing pressure distri‐  
bution in refrigerant circuit  
⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
Low pressure normal or too  
low (below specified value)  
•
The required cooling output  
is not attained solely at the  
evaporator for cooling the  
high-voltage components  
(the cooling output is OK at  
the evaporator in the front  
heater and air conditioning  
unit).  
♦ One of the pumps or valves in the high-  
voltage system's coolant circuit is de‐  
fective or does not function properly ⇒  
Heating, air conditioning; Rep. gr. 87 ;  
Coolant circuit (vehicle-specific Work‐  
shop Manual).  
Workshop Manual).  
– Check operation and activa‐  
tion of components for cool‐  
ing high-voltage compo‐  
nents ⇒ Vehicle diagnostic  
tester (“Guided Fault Find‐  
ing”).  
♦ Constriction or blockage in refrigerant – Extract refrigerant from re‐  
line to or from expansion valve at evap‐  
orator for cooling high-voltage compo‐  
nents  
frigerant circuit.  
– Check refrigerant line to ex‐  
pansion valve and clean or  
renew if necessary.  
♦ Expansion valve for evaporator for  
cooling high-voltage components de‐  
fective  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
Observe notes ⇒ page 259 .  
8. Checking pressures  
261  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible devia‐ Possible causes of  
Fault elimination  
tion from specifi‐  
cation  
fault  
•
High pres‐  
sure does not  
rise or only  
rises slightly  
above the  
♦ Air conditioner  
compressor is not  
activated or driv‐  
en.  
– Check activation  
and operation of air  
conditioner com‐  
pressor and per‐  
form servicing  
♦ One of the valves  
installed in the re‐  
frigerant circuit is  
defective or does  
not function prop‐  
erly ⇒ Heating,  
air conditioning;  
Rep. gr. 87 ; Re‐  
frigerant circuit  
(vehicle-specific  
Workshop Man‐  
ual).  
pressure with  
the engine  
stopped.  
⇒ Vehicle diagnos‐  
tic tester in “Guided  
Fault Finding”  
mode.  
•
•
Low pressure  
does not drop  
or only drops  
slightly.  
– Check operation  
and activation of  
the various valves  
installed in refriger‐  
ant circuit by ob‐  
serving pressure  
distribution in refrig‐  
erant circuit ⇒ Vehi‐  
cle diagnostic test‐  
er in “Guided Fault  
Finding” mode and  
⇒ Heating, air con‐  
ditioning; Rep. gr.  
87 ; Refrigerant cir‐  
cuit (vehicle-specif‐  
ic Workshop Man‐  
ual).  
Required  
cooling out‐  
put is not at‐  
tained in  
evaporator in  
air condition‐  
ing unit (and  
in evaporator  
for cooling  
high-voltage  
components)  
♦ Constriction or  
blockage in re‐  
frigerant circuit  
(e.g. in refrigerant  
line between  
– Clean refrigerant  
circuit (flush with re‐  
frigerant R134a)  
⇒ page 100 .  
service connec‐ – Renew hose or pipe  
tion on low-pres‐  
sure side and air  
conditioner com‐  
pressor).  
if kinked or constric‐  
ted.  
♦ Air conditioner  
compressor de‐  
fective  
– Renew air condi‐  
tioner compressor.  
Note  
Observe notes ⇒ page 259 .  
262  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from spec‐  
ification  
Possible causes of fault  
Fault elimination  
•
•
•
High pressure increases ♦ Activation or operation of air con‐ – Check activation and operation of air  
above specification  
ditioner compressor not OK  
conditioner compressor and perform  
servicing ⇒ Vehicle diagnostic tester  
in “Guided Fault Finding” mode.  
Low pressure drops quick‐ ♦ One of the valves installed in the  
ly to specified value  
refrigerant circuit is defective or  
does not function properly ⇒  
Heating, air conditioning; Rep.  
gr. 87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Manual).  
– Check operation and activation of  
the various valves installed in refrig‐  
erant circuit by observing pressure  
distribution in refrigerant circuit  
⇒ Vehicle diagnostic tester in “Gui‐  
ded Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehicle-spe‐  
cific Workshop Manual).  
Required cooling output is  
not attained in evaporator  
in front heater and air con‐  
ditioning unit (and/or in  
evaporator for cooling  
♦ Constriction or blockage in refrig‐  
erant circuit  
high-voltage components)  
♦ Expansion valve defective  
– Run hand over refrigerant circuit to  
check for differences in temperature.  
•
If there is a difference in temperature  
at one component:  
– Renew hose or pipe if kinked or con‐  
stricted.  
– In the event of a blockage, clean re‐  
frigerant circuit (flush with refrigerant  
R134a ⇒ page 100 ).  
– Re-charge refrigerant circuit.  
– Repeat test.  
8. Checking pressures  
263  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ If the expansion valve at the evaporator in the heater and air  
conditioning unit or the shut-off valve installed upstream is de‐  
fective (is permanently closed or does not open sufficiently),  
the air conditioner compressor is activated to maximum output  
and the low pressure drops to the specified value or below (air  
conditioner compressor draws off refrigerant from low-pres‐  
sure side). However, as no refrigerant (or an insufficient  
amount) can flow via the expansion valve, the cooling output  
is not attained and the high pressure may also not increase or  
only increase slightly since there is no energy exchange ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 00 ; Repair instructions;  
Checking cooling output (vehicle-specific Workshop Manual).  
♦ If the expansion valve upstream of the evaporator for cooling  
the high-voltage components is defective (or its operation or  
activation is faulty), permanently closed or does not open suf‐  
ficiently, the air conditioner compressor is also activated to  
maximum output (the required temperatures in the heat ex‐  
changer are not reached). The pressure on the low-pressure  
side then only drops to or below the specified value if no cool‐  
ing output is requested in the front heater and air conditioning  
unit at the same time. The air conditioner compressor draws  
off the refrigerant from the low-pressure side of both evapo‐  
rators. However, as no refrigerant can flow via the expansion  
valve in the front heater and air conditioning unit, and the cool‐  
ing output is not reached in the evaporator for cooling the high-  
voltage components (there is a fault in the area of the  
evaporator for cooling the high-voltage components), the elec‐  
tric air conditioner compressor is activated at a higher speed.  
However, as no more refrigerant can flow, the pressure on the  
low-pressure side drops below the specified value and the  
high pressure may also not increase or only increase slightly  
since there is no energy exchange. The same applies if a valve  
in the refrigerant circuit is not OK, if there is a fault in the in‐  
corporation of the evaporator for cooling the high-voltage com‐  
ponents in the high-voltage system's coolant circuit, or if a  
pump installed there or a valve is not OK. Although the high-  
voltage battery heat exchanger is cooled, the coolant does not  
reach the high-voltage components which need to be cooled  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Coolant circuit  
(vehicle-specific Workshop Manual).  
♦ Further notes ⇒ page 259  
264  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
•
•
•
High and low pressure nor‐ ♦ Activation of air conditioner compres‐ – Check activation and opera‐  
mal at first, but after a while:  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor and perform servic‐  
ing ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode.  
High pressure rises above  
specified value  
♦ One of the valves installed in the re‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
Low pressure drops to  
specified value or below  
– Check operation and activa‐  
tion of the various valves in‐  
stalled in refrigerant circuit  
by observing pressure distri‐  
bution in refrigerant circuit  
⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and/or  
in evaporator for cooling  
high-voltage components)  
♦ Moisture in refrigerant circuit  
Or  
•
High and low pressure nor‐  
mal at first  
Workshop Manual).  
•
After driving for a while, low  
pressure drops below  
specified value (evaporator  
in air conditioning unit ices  
up)  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 ).  
– Renew receiver with dryer.  
– Evacuate refrigerant circuit  
for at least 3 hours.  
– Re-charge refrigerant circuit.  
– Repeat test.  
Note  
♦ It is not necessary at first to clean the refrigerant circuit (to flush  
it with refrigerant R134a ⇒ page 100 ) when this issue occurs  
as there is usually only a small quantity of moisture in the sys‐  
tem which can be removed by lengthy evacuation.  
♦ If an issue involving moisture in the refrigerant circuit only oc‐  
curs after a lengthy operating period or only infrequently (low  
pressure drops below specified value and evaporator ices up),  
it is sufficient to renew the dryer in the receiver (adjust quantity  
of refrigerant oil). Subsequently, evacuate refrigerant circuit  
for at least 3 hours.  
♦ In this case, the evaporator may ice up although the amount  
of refrigerant in the refrigerant circuit is OK.  
♦ A faulty evaporator output temperature sender - G263- or  
pressure/temperature sender can also cause the refrigerant  
circuit to ice up. If this issue occurs, you should therefore also  
check the measured valves of the various pressure/tempera‐  
ture senders in the refrigerant circuit ⇒ Vehicle diagnostic  
tester in “Guided Fault Finding” mode and ⇒ Heating, air con‐  
ditioning; Rep. gr. 00 ; Repair instructions; Checking cooling  
output (vehicle-specific Workshop Manual).  
♦ Further notes ⇒ page 259  
8. Checking pressures  
265  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
Possible causes of fault  
Fault elimination  
fication  
•
•
•
High pressure normal  
Low pressure too low  
♦ Activation of air conditioner compres‐ – Check activation and opera‐  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor and perform servic‐  
ing ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode.  
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and/or  
in evaporator for cooling  
high-voltage components)  
♦ One of the valves installed in the re‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
– Check operation and activa‐  
tion of the various valves in‐  
stalled in refrigerant circuit  
by observing pressure distri‐  
bution in refrigerant circuit  
⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
and ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Refrigerant  
circuit (vehicle-specific  
♦ One of the pressure/temperature send‐  
ers in the refrigerant circuit is supplying  
incorrect values  
Workshop Manual).  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 ).  
♦ Shut-off valve upstream of expansion – Clean refrigerant circuit  
valve for evaporator in front heater and  
air conditioning unit defective  
(flush with refrigerant R134a  
⇒ page 100 ). Not always  
necessary; refer to notes.  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
– Renew expansion valve for  
evaporator in front heater  
and air conditioning unit and  
for receiver/dryer.  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK:  
– Renew air conditioner com‐  
pressor.  
– Re-charge refrigerant circuit.  
– Repeat test.  
266  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If the fault “High pressure normal, low pressure too low” oc‐  
curs, please note that the evaporator in the air conditioning  
unit may ice up although the amount of refrigerant in the circuit  
is OK.  
♦ If the fault is caused by the air conditioner compressor (the air  
conditioner compressor is activated at excessively high speed  
by the control unit for air conditioning compressor - J842- ), it  
is not necessary to clean the refrigerant circuit (to flush it with  
refrigerant R134a ⇒ page 100 ). In this case it is sufficient to  
renew the air conditioner compressor (observe quantity of re‐  
frigerant oil in compressor and adjust if necessary).  
♦ If the expansion valve upstream of the evaporator for cooling  
the high-voltage components is defective (or its operation or  
activation is faulty), permanently closed or does not open suf‐  
ficiently, the air conditioner compressor is also activated to  
maximum output (the required temperatures in the heat ex‐  
changer are not reached). The pressure on the low-pressure  
side then only drops to or below the specified value if no cool‐  
ing output is requested in the front heater and air conditioning  
unit at the same time. The air conditioner compressor draws  
off the refrigerant from the low-pressure side of both evapo‐  
rators. However, as no refrigerant can flow via the expansion  
valve in the front heater and air conditioning unit, and the cool‐  
ing output is not reached in the evaporator for cooling the high-  
voltage components (there is a fault in the area of the  
evaporator for cooling the high-voltage components), the elec‐  
tric air conditioner compressor is activated at a higher speed.  
However, as no more refrigerant can flow, the pressure on the  
low-pressure side drops below the specified value and the  
high pressure may also not increase or only increase slightly  
since there is no energy exchange. The same applies if a valve  
in the refrigerant circuit is not OK, if there is a fault in the in‐  
corporation of the evaporator for cooling the high-voltage com‐  
ponents in the high-voltage system's coolant circuit, or if a  
pump installed there or a valve is not OK. Although the high-  
voltage battery heat exchanger is cooled, the coolant does not  
reach the high-voltage components which need to be cooled  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 87 ; Coolant circuit  
(vehicle-specific Workshop Manual).  
♦ A faulty evaporator output temperature sender - G263- or  
pressure/temperature sender can also cause this issue. You  
should therefore also check the measured valves of the vari‐  
ous pressure/temperature senders in the refrigerant circuit  
⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode  
and ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐  
tions; Checking cooling output (vehicle-specific Workshop  
Manual).  
♦ Further notes ⇒ page 259  
8. Checking pressures  
267  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High pressure normal or too ♦ Activation of air conditioner compres‐ – Check activation and opera‐  
high  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor and perform servic‐  
ing ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode.  
•
•
Low pressure too high  
♦ One of the valves installed in the re‐  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
Noise from air conditioner  
compressor (particularly af‐  
ter being switched on)  
– Check operation and activa‐  
tion of the various valves and  
pressure/temperature send‐  
ers installed in refrigerant cir‐  
cuit by observing pressure  
distribution in refrigerant cir‐  
cuit ⇒ Vehicle diagnostic  
•
Required cooling output is  
not attained in evaporator in  
front heater and air condi‐  
tioning unit and/or in evap‐  
orator for cooling high-volt‐  
age components  
♦ One of the pressure/temperature send‐  
ers in the refrigerant circuit is supplying  
incorrect values  
tester in “Guided Fault Find‐  
ing” mode and ⇒ Heating, air  
conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-  
specific Workshop Manual).  
♦ Too much refrigerant in circuit  
– Extract refrigerant from re‐  
frigerant circuit.  
•
If quantity of refrigerant ex‐  
tracted is significantly great‐  
er than specified capacity:  
– Re-charge refrigerant circuit.  
– Repeat test.  
•
The quantity of refrigerant  
extracted corresponds  
roughly to the actual capaci‐  
ty.  
– Check activation and opera‐  
tion of air conditioner com‐  
pressor and of valves instal‐  
led in refrigerant circuit (see  
below).  
♦ Shut-off valve upstream of expansion – Check shut-off valve ⇒ Heat‐  
valve for evaporator in front heater and  
air conditioning unit defective  
ing, air conditioning; Rep. gr.  
87 ; Refrigerant circuit (vehi‐  
cle-specific Workshop Man‐  
ual).  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
– Renew expansion valve for  
evaporator in front heater  
and air conditioning unit and  
for receiver/dryer.  
♦ Air conditioner compressor defective  
– Re-charge refrigerant circuit.  
– Repeat test if operation is not  
OK.  
– Renew air conditioner com‐  
pressor.  
268  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ This fault may also be caused by too much refrigerant oil in  
the circuit. Overfilling with refrigerant oil may occur if, for ex‐  
ample, the air conditioner compressor has been renewed  
without adjusting the quantity of refrigerant oil.  
♦ Further notes ⇒ page 259  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High and low pressure nor‐ ♦ Activation of air conditioner compres‐ – Check activation and opera‐  
mal  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor and perform servic‐  
ing ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode.  
•
Required cooling output is  
not attained in evaporator in ♦ One of the valves installed in the re‐  
air conditioning unit (and in  
evaporator for cooling high-  
voltage components)  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
– Check operation and activa‐  
tion of the various valves and  
pressure/temperature send‐  
ers installed in refrigerant cir‐  
cuit by observing pressure  
distribution in refrigerant cir‐  
cuit ⇒ Vehicle diagnostic  
Or  
•
High and low pressure nor‐ ♦ One of the pressure/temperature send‐  
mal  
ers in the refrigerant circuit is supplying  
incorrect values  
•
•
Noise from air conditioner  
compressor (particularly af‐  
ter being switched on)  
tester in “Guided Fault Find‐  
ing” mode and ⇒ Heating, air  
conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-  
specific Workshop Manual).  
Required cooling output is  
not attained in evaporator in  
air conditioning unit (and/or  
in evaporator for cooling  
high-voltage components)  
♦ Too much refrigerant in circuit  
– Discharge refrigerant circuit.  
♦ Expansion valve for evaporator in front  
heater and air conditioning unit defec‐  
tive  
– Clean refrigerant circuit  
(flush with refrigerant R134a  
⇒ page 100 ).  
♦ Too much refrigerant oil in circuit  
– Add correct quantity of refrig‐  
erant oil to circuit (refer to  
note).  
– Re-charge refrigerant circuit.  
– Repeat test.  
8. Checking pressures  
269  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ Overfilling with refrigerant oil may occur if, for example, the air  
conditioner compressor has been renewed without adjusting  
the quantity of refrigerant oil.  
♦ If, for example, the expansion valve for the evaporator in the  
air conditioning unit or for the evaporator for cooling the high-  
voltage components is defective (permanently open), the  
evaporator temperature (in the front heater and air condition‐  
ing unit or in the evaporator for cooling the high-voltage com‐  
ponents) is no longer regulated such that the refrigerant  
emerging from the evaporator outlet is in gaseous form only.  
Under certain usage conditions, liquid droplets may then be  
drawn in by the air conditioner compressor and result in noise  
(liquid cannot be compressed).  
♦ If there is too much refrigerant oil in the circuit, discharge the  
air conditioner compressor and renew the receiver. After  
cleaning the refrigerant circuit (flushing with refrigerant R134a  
⇒ page 100 ), add the correct amount of refrigerant oil to the  
circuit ⇒ page 333 .  
♦ Further notes ⇒ page 259  
Possible deviation from speci‐  
fication  
Possible causes of fault  
Fault elimination  
•
High and low pressure nor‐ ♦ Activation of air conditioner compres‐ – Check activation and opera‐  
mal  
sor faulty ⇒ Vehicle diagnostic tester in  
“Guided Fault Finding” mode  
tion of air conditioner com‐  
pressor and perform servic‐  
ing ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode.  
•
Required cooling output is  
not attained in evaporator at ♦ One of the valves installed in the re‐  
front heater and air condi‐  
tioning unit (and at evapo‐  
rator for cooling high-volt‐  
age components)  
frigerant circuit is defective or does not  
function properly ⇒ Heating, air condi‐  
tioning; Rep. gr. 87 ; Refrigerant circuit  
(vehicle-specific Workshop Manual).  
– Check operation and activa‐  
tion of the various valves and  
pressure/temperature send‐  
ers installed in refrigerant cir‐  
cuit by observing pressure  
distribution in refrigerant cir‐  
cuit ⇒ Vehicle diagnostic  
•
Required cooling output is ♦ One of the pressure/temperature send‐  
not attained at evaporator  
for heat pump operation  
ers in the refrigerant circuit is supplying  
incorrect values  
tester in “Guided Fault Find‐  
ing” mode and ⇒ Heating, air  
conditioning; Rep. gr. 87 ;  
Refrigerant circuit (vehicle-  
specific Workshop Manual).  
One of the pumps or valves in the high- – Check operation and activa‐  
voltage system's coolant circuit or the en‐  
gine coolant circuit is defective or does not  
function properly ⇒ Heating, air condition‐  
ing; Rep. gr. 87 ; Coolant circuit (vehicle-  
specific Workshop Manual).  
tion of components for cool‐  
ing high-voltage compo‐  
nents ⇒ Vehicle diagnostic  
tester in “Guided Fault Find‐  
ing” mode for air conditioner,  
air conditioner compressor  
and battery regulation.  
– Check incorporation of heat  
exchanger into engine cool‐  
ant circuit and function and  
activation of the various  
pumps and valves ⇒ Heat‐  
ing, air conditioning; Rep. gr.  
87 ; Coolant circuit .  
270  
Rep. gr.87 - Air conditioning system  
Audi 100 1991 ➤ , Audi 80 1992 ➤ , Audi A1 2011 ➤ , Audi A1 Sportback 2 ...  
Air conditioner with refrigerant R134a - Edition 11.2018  
Note  
♦ If the required cooling output of the evaporator in the front  
heater and air conditioning unit (and the evaporator for cooling  
the high-voltage components) is OK and there is a problem  
due to a lack of heating output at the heat exchanger for heat  
pump operation. The cause may lie in the coolant circuit of the  
high-voltage system or the engine coolant circuit. If the pumps  
and valves in the high-voltage system's coolant circuit are not  
activated correctly or if their operation is not OK, not enough  
heat energy can be absorbed from the coolant via the evapo‐  
rator (heat exchanger) for the high-voltage system compo‐  
nents. If the pumps and valves in the engine coolant circuit are  
not activated correctly or if their operation is not OK, the ab‐  
sorbed heat energy cannot be transferred via the heat ex‐  
changer for heat pump function to the coolant flowing to the  
heat exchanger in the heater and air conditioning unit ⇒ Ve‐  
hicle diagnostic tester in “Guided Fault Finding” mode and ⇒  
Heating, air conditioning; Rep. gr. 87 ; Coolant circuit (vehicle-  
specific Workshop Manual).  
♦ Further notes ⇒ page 259  
8. Checking pressures  
271  

Related Topics

Checking pressures in refrigerant circuit with air conditioner service station (with ignition switched off)
Checking pressures - vehicles with restrictor and reservoir (with internally regulated air conditioner compressor)
Checking pressures - vehicles with expansion valve and receiver (with internally regulated air conditioner compressor)
Checking pressures - vehicles with restrictor, reservoir and air conditioner compressor regulating valve N280 (with externally regulated air conditioner compressor)
Checking pressures - vehicles with expansion valve, receiver and air conditioner compressor regulating valve N280 (with externally regulated air conditioner compressor)
Checking pressures - vehicles with electrically driven air conditioner compressor (vehicles with high-voltage system)

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