Get Air conditioning system -> 2.14.3 Checking pressures in the refrigerant circuit with the ignition switched off Guide for Volkswagen Touran 4 Door Second Generation (2015-2022)

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Under certain operating conditions, residual moisture in the re‐

frigerant circuit may lead to the formation of ice at the air condi‐

tioner compressor regulating valve. The ice impairs the air

conditioner compressor control and causes the evaporator to be

cooled excessively and to ice up. Icing-up of the evaporator may

give rise to the following problems:

♦ Repeated or sporadic failure of the air conditioner (no cooling/

heat output) after a lengthy journey. After switching off the en‐

gine and waiting for a short period, operation of air conditioner

returns to normal.

♦ Misting up of the windows on the inside after a long journey;

the windows are initially not cleared even by pressing the De-

frost button; the air conditioner functions properly again after

a short delay following engine shut-off (or after switching off

the air conditioner).

Remedy:

– On vehicles with an air conditioner compressor with air con‐

ditioner compressor regulating valve - N280- , check the

measured value of the evaporator output temperature sender

- G263- (via the “Read measured values” function). If the

measured value of the sender is too low under the operating

conditions described by the customer (at an ambient temper‐

ature above 0°C, colder than 0°C for an extended period even

though the -N280- is currently not actuated) or too high (higher

than approx. 10°C, even though the air conditioning system is

functioning properly): the evaporator may ice up due to the

incorrect measured value ⇒ Vehicle diagnostic tester in “Gui‐

ded Fault Finding” mode - air conditioning system and ⇒

Heating, air conditioning; Rep. gr. 00 ; Repair instructions;

Checking cooling output (vehicle-specific workshop manual).

– On vehicles without evaporator output temperature sender -

G263- , use e.g. the footwell vent temperature sender - G192-

to check the outlet temperature with the temperature set to

“low” or “cold” for the driver and front passenger side with the

lowest setting (4 or 5 bars) for the fresh air blower speed, air

outlet in the footwell and fresh air mode under the operating

conditions described by the customer. If the measured value

of the sender is too low (with an ambient temperature higher

than 0°C, colder than 0°C for an extended period), the evap‐

orator could ice up due to the wrong measured value ⇒ Vehicle

diagnostic tester in “Guided Fault Finding” mode - air condi‐

tioning system.

– On vehicles with shut-off valves in the refrigerant circuit, check

the function and actuation of these valves ⇒ Vehicle diagnostic

tester in “Guided Fault Finding” mode - air conditioning sys‐

tem, ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant

circuit; System overview - refrigerant circuit and ⇒ Heating,

air conditioning; Rep. gr. 00 ; Repair instructions; Checking

cooling output (vehicle-specific workshop manual).

– Check the refrigerant line from the evaporator (or from the in‐

ner heat exchanger) and the air conditioner compressor (thick

pipe, low pressure side) with the engine running. If this line is

very icy when the complaint is encountered (a thin layer of ice

is acceptable), this is also evidence that the temperature in the

evaporator is too low ⇒ Heating, air conditioning; Rep. gr. 87 ;

Refrigerant circuit; System overview - refrigerant circuit (vehi‐

cle-specific workshop manual).

– Empty the refrigerant circuit, renew the receiver with dryer,

renew the reservoir with dryer or desiccant cartridge and then

evacuate the refrigerant circuit for at least 3 hours ⇒ Heating,

air conditioning; Rep. gr. 87 ; Refrigerant circuit; System over‐

view - refrigerant circuit (vehicle-specific workshop manual)

and ⇒ page 129 .

172

Rep. gr.87 - Air conditioning system

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

♦ ⇒ “2.14.3 Checking pressures in the refrigerant circuit with the

ignition switched off”, page 176

♦ ⇒ “2.14.4 Checking pressures with air conditioning system

switched on - vehicles with mechanical air conditioning com‐

pressor”, page 183 .

♦ ⇒ “2.14.5 Checking pressures with air conditioning system

switched on - vehicles with electrical air conditioning com‐

pressor”, page 205

2.14.2

Pressures and temperatures in refriger‐

ant circuit

General information about pressures and temperatures in the re‐

frigerant circuit ⇒ page 173

Pressures and temperatures in refrigerant circuit with expansion

valve ⇒ page 174

General information about pressures and temperatures in the re‐

frigerant circuit

♦ The pressures and temperatures in the refrigerant circuit de‐

pend on the current operating conditions (e.g. engine speed,

radiator running at level 1, 2, or 3, engine temperature, air

conditioner compressor actuation on or off) as well as envi‐

ronmental influences (e.g. ambient temperature, humidity, re‐

quired cooling output).

♦ On vehicles with air conditioner compressor regulating valve -

N280- , the pressure on the low pressure side is varied by

means of -N280- actuation.

♦ For these reasons, the values given in the following table may

only be considered guidelines. They occur at an engine speed

of 1,500 to 2,000 rpm and an ambient temperature of 20°C

after about 20 minutes.

♦ Refer to the vehicle-specific refrigerant circuit for the pressure

gauge set measurement connections ⇒ Heating, air condi‐

tioning; Rep. gr. 87 ; Refrigerant circuit (vehicle-specific work‐

shop manual).

♦ At 20°C and with the engine stationary, the refrigerant circuit

will adjust itself to a pressure of 4.7 bar overpressure

⇒ “6.1.3 Vapour pressure table for refrigerant”, page 17 (va‐

pour pressure table).

Note

♦ Pressure is indicated in various units: 1 MPa (Mega-Pascal)

is equal to 10 bar or 145 psi; 1 bar absolute pressure is equal

to 0 bar, which is about the same as ambient pressure (at‐

mospheric pressure).

♦ The pressures and temperatures in refrigerant circuits with re‐

strictor and reservoir are about the same as those in refriger‐

ant circuits with expansion valve. Since Volkswagen/Audi

currently only installs refrigerant circuits with expansion valve,

just this refrigerant circuit is described here.

2. Working with air conditioner service station

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Pressures and temperatures in refrigerant circuit with expansion

valve

Note

♦ The following log (p), h-diagram (logarithmic pressure, energy

diagram) shows the processes that run during certain operat‐

ing conditions in the refrigerant circuit. These values change

depending on the environmental conditions (engine speed,

ambient temperature, requisite cooling output, etc.).

♦ The log (p), h-diagram shows the pressure (0 to 60 in bar ab‐

solute pressure) and the energy content (100 to 420, specific

enthalpy in kilojoules per kg of R1234yf refrigerant) in the re‐

frigerant circuit cycle.

♦ The arrows indicate the direction of refrigerant flow in the re‐

frigerant circuit.

A - Area with vaporous refrigerant

B - Area with gaseous refrigerant

C - Area with liquefied refrigerant

D - Supercritical pressure and temperature range, physical state

of refrigerant undetermined (no longer a separation between liq‐

uefied and gaseous refrigerant)

1 - Low pressure side: output of inner heat exchanger, input of

air conditioner compressor, refrigerant is completely evapo‐

rated and gaseous, temperature of refrigerant is approx. -4°

2 - High pressure side: output of air conditioner compressor,

input of condenser, refrigerant has been compressed and is

gaseous, temperature of refrigerant is up to approx. 80°C

3 - High pressure side: output of condenser (receiver), input of

inner heat exchanger, refrigerant has been cooled down and

is liquefied, temperature of refrigerant is approx. 55°C

4 - High pressure side: output of inner heat exchanger, input of

expansion valve, liquefied refrigerant has cooled down fur‐

ther, temperature of refrigerant is approx. 50°C

5 - Low pressure side: expansion valve on evaporator side, in‐

put of evaporator, liquefied refrigerant comes to rest and

starts to evaporate, temperature of refrigerant approx. -7°C

6 - Low pressure side: output of evaporator, expansion valve,

input of inner heat exchanger, refrigerant mainly evapora‐

ted, small percentage is still vaporous, temperature of re‐

frigerant approx. -6°C

174

Rep. gr.87 - Air conditioning system

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Note

♦ The temperatures given relate to the refrigerant in the refrig‐

erant circuit. The temperatures deviate from this on the sur‐

face of components containing refrigerant owing to heat

absorption and dissipation.

♦ The pressure and the temperature, too, are maintained at ap‐

prox. 3 bar absolute pressure (equates to approx. 2 bar over‐

pressure) in refrigerant circuits with regulated air conditioner

compressor despite thermal changes and different engine

speeds. This applies however only within the rated range of

the air conditioner compressor; if the rated range of the air

conditioner compressor is exceeded, the pressure will in‐

crease and so, too, will the temperature

⇒ “2.14 Checking pressures”, page 170 .

♦ On air conditioner compressors that do not regulate their per‐

formance themselves, the pressure on the low pressure side

and thereby the evaporator temperature are regulated by the

respective control via the air conditioner compressor regulat‐

ing valve - N280- . Depending on the version and the setting,

if an air temperature of less than approx. 2°C is measured after

the evaporator, the performance of the air conditioner com‐

pressor is lowered. At below 0°C, -N280- actuation is switched

off. This prevents the evaporator from cooling down too much

and becoming icy.

♦ On vehicles with two evaporators and two expansion valves,

the temperature and pressure in the refrigerant circuit are the

same at the second evaporator as those in vehicles with only

one evaporator and one expansion valve (parallel circuit).

♦ Depending on the version of refrigerant circuit, a component

with inner heat exchanger may be installed. In the internal heat

exchanger, the hot liquid refrigerant flowing on the high pres‐

sure side supplies energy to the cold gaseous or vaporous

refrigerant flowing on the low pressure side, thus enhancing

the efficiency of the air conditioner

⇒ “1.2.13 Refrigerant line with internal heat exchanger”, page

51 .

♦ Depending on the version of control unit (e.g. operating and

display unit for front air conditioning system - E87- or Clima‐

tronic control unit - J255- ), the measured ambient conditions

(exterior temperature, moisture in the passenger compartment

etc.) and the control unit setting (passenger compartment tem‐

perature, operating mode etc.), the pressure and thereby also

the temperature at the output of the evaporator can also be

regulated at a higher temperature ⇒ Vehicle diagnostic tester

in “Guided Fault Finding” mode - air conditioning system.

2. Working with air conditioner service station

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

2.14.3

Checking pressures in the refrigerant

circuit with the ignition switched off

Test prerequisites ⇒ page 176

Checking pressures with the ignition switched off ⇒ page 179

Conditions for testing

Note

♦ Work on the refrigerant circuit that involves the air conditioner

service station (checking the pressures in this case) can usu‐

ally be carried out without the need to de-energise the high-

voltage system.

♦ Only de-energise the high-voltage system if work on the high-

voltage system is necessary ⇒ page 3

All vehicles

Note

♦ Certain conditions for testing are pertinent to a certain vehicle

and are described in the vehicle-specific workshop manual ⇒ ^lk

Heating, air conditioning; Rep. gr. 00 ; Repair instructions;

Checking cooling output (vehicle-specific workshop manual).

♦ Depending on the version of air conditioner compressor, a

valve may be installed on the high-pressure side that prevents

liquefied refrigerant flowing back into the air conditioner com‐

pressor after the air conditioning system is switched off. If an

air conditioner compressor with this valve is installed in a ve‐

hicle with a refrigerant circuit with expansion valve, it could

take some time before the pressure on the high-pressure side

drops (the expansion valve is cold and the pressure on the

low-pressure side rises quickly after switching off, the expan‐

sion valve closes and refrigerant only flows slowly on the low-

pressure side). If the air conditioner compressor is switched

on, the pressure on the low-pressure side drops, the expan‐

sion valve opens and refrigerant can flow on the low-pressure

side.

♦ Check the cooling output ⇒ Heating, air conditioning; Rep. gr.

00 ; Repair instructions; Checking cooling output (vehicle-spe‐

cific workshop manual).

♦ Connections with valve and service connections for measuring

and testing ⇒ Heating, air conditioning; Rep. gr. 87 ; Refrig‐

erant circuit (vehicle-specific workshop manual).

♦ Connect the air conditioner service station

⇒ “2.2 Connecting air conditioner service station to refrigerant

circuit”, page 131 .

Under certain operating conditions, residual moisture in the re‐

frigerant circuit may lead to the formation of ice at the air condi‐

tioner compressor regulating valve. The ice impairs the air

conditioner compressor control and causes the evaporator to be

cooled excessively and to ice up. Icing-up of the evaporator may

give rise to the following problems:

♦ Repeated or sporadic failure of the air conditioner (no cooling/

heat output) after a lengthy journey. After switching off the en‐

gine and waiting for a short period, operation of air conditioner

returns to normal.

176

Rep. gr.87 - Air conditioning system

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

♦ Misting up of the windows on the inside after a long journey;

the windows are initially not cleared even by pressing the De-

frost button; the air conditioner functions properly again after

a short delay following engine shut-off (or after switching off

the air conditioner).

Remedy:

– On vehicles with an air conditioner compressor with air con‐

ditioner compressor regulating valve - N280- ,_lkcheck the

measured value of the evaporator output temperature sender

- G263- (via the “Read measured values” function). If the

measured value of the sender is too low under the operating

conditions described by the customer (at an ambient temper‐

ature above 0°C, colder than 0°C for an extended period even

though the -N280- is currently not actuated) or too high (higher

than approx. 10°C, even though the air conditioning system is

functioning properly): the evaporator may ice up due to incor‐

rect actuation of -N280- or the incorrect measured value of -

G263- ⇒ Vehicle diagnostic tester in “Guided Fault Finding”

mode - air conditioning system and ⇒ Heating, air condition‐

ing; Rep. gr. 00 ; Repair instructions; Checking cooling output

(vehicle-specific workshop manual).

– On vehicles without evaporator output temperature sender -

G263- , use e.g. the footwell vent temperature sender - G192-

to check the outlet temperature with the temperature set to

“low” or “cold” for the driver and front passenger side with the

lowest setting (4 or 5 bars) for the fresh air blower speed, air

outlet in the footwell and fresh air mode under the operating

conditions described by the customer. If the measured value

of the sender is too low (with an ambient temperature higher

than 0°C, colder than 0°C for an extended period), the evap‐

orator could ice up due to the wrong measured value ⇒ Vehicle

diagnostic tester in “Guided Fault Finding” mode - air condi‐

tioning system.

– On vehicles with shut-off valves in the refrigerant circuit, check

the function and actuation of these valves ⇒ Vehicle diagnostic

tester in “Guided Fault Finding” mode - air conditioning system

⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit

(vehicle-specific workshop manual) and ⇒ Heating, air con‐

ditioning; Rep. gr. 00 ; Repair instructions; Checking cooling

output (vehicle-specific workshop manual).

– Check the refrigerant line from the evaporator (or from the in‐

ner heat exchanger) and the air conditioner compressor (thick

pipe, low pressure side) with the engine running. If this line is

very icy when the complaint is encountered (a thin layer of ice

is acceptable), this is also evidence that the temperature in the

evaporator is too low ⇒ Heating, air conditioning; Rep. gr. 87 ;

Refrigerant circuit (vehicle-specific workshop manual).

– Empty the refrigerant circuit, renew all reservoirs/receivers

with dryer or desiccant cartridge and then evacuate the refrig‐

erant circuit for at least 3 hours ⇒ Heating, air conditioning;

Rep. gr. 87 ; Refrigerant circuit (vehicle-specific workshop

manual) and

⇒ “2 Working with air conditioner service station”, page 129 .

Conditions for testing

♦ Observe the general information on checking pressures in the

refrigerant circuit

⇒ “2.14.1 General information on checking pressures in the

refrigerant circuit”, page 170

2. Working with air conditioner service station

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Air conditioning systems with refrigerant R1234yf - General information - Edition 07.2017

Note

All of the conditions for testing marked with * are pertinent to a

certain vehicle and are described in the vehicle-specific workshop

manual ⇒ Heating, air conditioning; Rep. gr. 00 ; Repair instruc‐

tions; Checking cooling output (vehicle-specific workshop man‐

ual).

General conditions for testing (these only have an influence on

the display of the pressure gauges during this measurement with

the air conditioning system switched on)

•

Radiator and condenser are clean (clean them if necessary).*

The heat insulation on the expansion valve is OK and properly

installed.*

•

The poly V-belt is OK and properly tensioned. The belts for air

conditioner compressor and alternator are in good condition

and correctly tensioned.*

The drive unit for the air conditioner compressor is OK and

properly installed.*

•

All air ducts, covers and seals are OK and properly installed.*

Diagnosis of the air conditioning system finds no faults (with

the engine running and the air conditioning system switched

on), no compressor deactivation conditions are shown in the

measured values (only on vehicles with diagnosis “air condi‐

tioning system”).* ⇒ Vehicle diagnostic tester in “Guided Fault

Finding” mode of air conditioning system.

•

The air flow rate through the dust and pollen filter is not im‐

paired by dirt.*

All dash panel air vents are open.*

Note

♦ Depending on the engine, the air conditioner compressor is

driven by different components (belts or drive shaft). To pro‐

tect these components and the engine, the pulley or the air

conditioner compressor drive unit is fitted with an overload

protection which is tripped if the air conditioner compressor is

not operating smoothly ⇒ Heating, air conditioning; Rep. gr.

00 ; Repair instructions; Checking cooling output (vehicle-spe‐

cific workshop manual) and ⇒ Heating, air conditioning; Rep.

gr. 87 ; Air conditioner compressor (vehicle-specific workshop

manual).

♦ On certain versions, the radiator fan cuts in only after the pres‐

sure in the refrigerant circuit has exceeded a pre-set value

⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -

air conditioning system.

Other conditions for testing (these have an influence on the dis‐

play of the pressure gauge with this measurement)

•

The vehicle is not exposed to the sun's rays ⇒ Heating, air

conditioning; Rep. gr. 00 ; Repair instructions; Checking cool‐

ing output (vehicle-specific workshop manual).

•

Ambient temperature is above 15°C.

The ignition is switched off.

The air conditioner service station is connected to the refrig‐

erant circuit

178

Rep. gr.87 - Air conditioning system

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⇒ “2.2 Connecting air conditioner service station to refrigerant

circuit”, page 131 .

♦ ⇒ “2.14.4 Checking pressures with air conditioning system

switched on - vehicles with mechanical air conditioning com‐

pressor”, page 183 .

♦ ⇒ “2.14.5 Checking pressures with air conditioning system

switched on - vehicles with electrical air conditioning com‐

pressor”, page 205

Checking pressures with the ignition switched off

Note

♦ The switching pressures for actuation of the air conditioner

compressor regulating valve - N280- , the air conditioning sys‐

tem magnetic clutch - N25- (if fitted) and the radiator fan (e.g.

radiator fan - V7- / radiator fan 2 - V177- ) are vehicle-specific

⇒ Vehicle diagnostic tester in “Guided Fault Finding” mode -

air conditioning system.

♦ The pressures must be measured at the service connections;

the fitting locations of these connections are vehicle-specific

⇒ Heating, air conditioning; Rep. gr. 87 ; Refrigerant circuit

(vehicle-specific workshop manual).

♦ Once the planned measures are complete, separate the air

conditioner service station from the refrigerant circuit and

switch it off

⇒ “2.8 Switching off air conditioner service station and sepa‐

rating from refrigerant circuit”, page 151 .

•

The engine is at operating temperature (at an ambient tem‐

perature less than 25°C).

Note

♦ Should the engine not be at operating temperature, take the

vehicle for a short drive.

♦ To test the cooling output, the engine does not have to be at

operating temperature. However, to demand a certain cooling

output from the air conditioning system at an ambient temper‐

ature of less than 25°C, the engine is required to be warm if

ambient temperatures are low.

♦ Observe the test prerequisites ⇒ page 176 .

– On vehicles with high-voltage system, switch off “stationary air

conditioning” function (deactivate)⇒ Owner's Manual and ⇒

Operating instructions of infotainment / MMI .

– Switch off ignition.

– Connect the air conditioner service station

⇒ “2.2 Connecting air conditioner service station to refrigerant

circuit”, page 131 .

– Check the pressures in the refrigerant circuit with the engine

stationary.

– Take pressure readings from pressure gauges of air condi‐

tioner service station . Two results may be displayed:

♦ The pressure in the refrigerant circuit is lower than indicated

in the following table ⇒ page 182 .

♦ The pressure in the refrigerant circuit is equal to or greater than

that in the following table ⇒ page 183 .

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Air conditioning system -> 2.14.3 Checking pressures in the refrigerant circuit with the ignition switched off for Your Volkswagen Touran 4 Door Second Generation (2015-2022)

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