Audi A4: Refrigerant Circuit, Checking Pressure with Service Station
General Information
Note
- All test conditions marked * are vehicle-specific and are
described in the Repair Manual for the relevant vehicle.
- Check cooling performance.
- Connections with valve and service connections for
measurement and testing. Refer to
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit (vehicle-specific
repair manual).
- Depending on the A/C compressor version, there may be a
valve installed on the high pressure side of the A/C compressor,
which prevents the liquid refrigerant from flowing back into the
compressor once the A/C is turned off. If an A/C compressor with
this valve is installed in a vehicle with a refrigerant circuit
having an expansion valve, then it may take some time until the
pressure in the high pressure side decreases (the expansion is
cold and the pressure in the low pressure side quickly increases
after it is turned off, the expansion valve closes and the
refrigerant flows slowly into the low pressure side). If the A/C
compressor is switched on, the pressure on the low pressure side
goes down, the expansion valve open and the refrigerant can flow
of the low pressure side.
Under certain operating conditions, residual moisture in
refrigerant circuit can lead to an ice build-up at A/C
Compressor Regulator Valve. A/C compressor control is reduced by
this ice build-up, evaporator is cooled too intensely and
freezes. The freeze-up of the evaporator can be the cause for
the following customer complaints:
- After a long drive, A/C system repeatedly or sporadically
fails (no cooling or heating performance). After switching off
the vehicle and after a short time, A/C function is OK again.
- After a long drive, windows (front/side and rear windows)
fog up from inside, windows are also not cleared by then
pressing the Defrost button, after
switching off vehicle and after a short time, A/C function is OK
again.
Corrective Action:
- On vehicles as of model year 2001 equipped with a compressor
with A/C Compressor Regulator Valve -N280-, check measured value
of evaporator outflow temperature Evaporator Vent Temperature
Sensor -G263- (via function "Read measuring value block"). Is
the measured value from the sensor is below the operating
condition described by the customer (at an temperature above 0
ºC (32 ºF), longer when it is lower than 0 ºC (32 ºF) although
the A/C Compressor Regulator Valve -N280- is not currently
activated) or too high (above 10 ºC (50 ºF) even though the A/C
is working correctly). Can ice up caused by the incorrect
measured value from the evaporator. Use the Vehicle Diagnostic
Tester ("OBD" or "Guided Fault Finding for the A/C system") and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit (vehicle-specific
repair manual).
- In vehicles without the Evaporator Vent Temperature Sensor
-G263-, for example via the Footwell Vent Temperature Sensor
-G192-, check vent temperature at the adjustment: "Lo
temperature" for driver and passenger side, 4 or 5 bar (58 or 73
psi) for fresh air blower RPM, air outlet in footwell and fresh
air operation under operating conditions specified by customer.
If measured value of sensor is too low (at ambient temperature
above 0 ºC (32 ºF), colder than 0 ºC (32 ºF) for a long period
of time).
- Check refrigerant line from evaporator to accumulator (thick
tube, low pressure side) with engine running. If this line is
thickly iced-up when complaint occurs (a thin layer of ice is
permitted), this also indicates that the temperature in the
evaporator is too low.
- Discharge refrigerant circuit, replace accumulator or
receiver/dryer with dryer and evacuate refrigerant circuit for a
minimum of three hours.
Test Requirements
Note
The following are the test requirements for a vehicle with a
mechanically driven A/C compressor as an example. On vehicles
with a high-voltage system (for example Audi A3 e-tron, Audi Q7
e-tron etc.) and/or the additional A/C functions (for example
Audi Q7 e-tron) this arrangement varies. Pay attention on these
vehicles to the specifications in the respective repair manuals
and the Guided Fault Finding. Refer to
→ Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair
Instructions; Checking Cooling Output and use the
Vehicle Diagnostic Tester in the "Guided Fault Finding"
function.
- Radiator and condenser are clean (clean if necessary).
- The thermal insulation at expansion valve is OK and properly
installed *
- Ribbed belt is OK and properly tensioned. Ribbed belt for
A/C compressor and generator are OK and correctly tensioned *
- All air ducts, covers and seals are OK and properly
installed.
- Fault finding on the electrical equipment and vacuum system
found no malfunction * Vehicle Diagnostic Tester ("OBD" or
"Guided Fault Finding" for the A/C system) and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit (vehicle-specific
repair manual).
- Air conditioner On Board Diagnostic (OBD) has not revealed
any faults (with engine running and air conditioner switched
on), no compressor shutoff criterion displayed in measured value
block (vehicles with "Air conditioner" On Board Diagnostic only)
*. Use the Vehicle Diagnostic Tester ("OBD" or "Guided Fault
Finding") and
→ Heating, Ventilation, Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit vehicle-specific
Repair Manual).
- Air flow through dust and pollen filter not obstructed by dirtю
- Air conditioner 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 doors in air conditioner unit, heater and evaporator
reach end position *
- Fresh-air intake ducts beneath hood and in passenger
compartment as well as corresponding water drain valves OK *.
Refer to
→ Heating, Ventilation, Air Conditioning; Rep. Gr.87; Air Guide
(vehicle-specific repair manual)
- The engine is warm
- Vehicle is not exposed to direct sunlight. Refer to
→ Heating, Ventilation and Air Conditioning; Rep. Gr.00; Repair
Instructions; Checking Cooling Output
(vehicle-specific repair manual)
- The ambient temperature is greater than 15 ºC (59 ºF).
- All instrument panel vents are open.
- Start the engine.
Settings on the A/C system control module on the A/C Control
Head -E87- or Climatronic Control Module -J255- (and Rear A/C
Control Head (Climatronic) -E265- in vehicles with two A/C
units):
- Preselect "Auto" mode (A/C compressor on).
- Set temperature pre-selector switch to "LO" for driver's
side and front passenger's side (and the rear of the vehicle
interior, left and right in vehicles with two A/C units).
Setting on heater controls:
- Press A/C button and Rec- or recirculated air button.
- Turn rotary temperature control towards "cold" stop.
- Set rotary fresh-air blower control to "4".
The following system test conditions should be met:
- One or more Radiator Fan -V7- (Radiator Fan 2 -V177-)
operated (at least speed 1)*
Note
For some versions, the fan is switched on only once the
pressure in refrigerant circuit has exceeded a specified value.
- Fresh Air Blower -V2- (and Rear Fresh Air Blower -V80- in
vehicles with two A/C units) running at maximum speed.
- Recirculated/fresh-air door set to "Recirculated air mode"
(within one minute, after starting vehicle, air-flow door is
closed and recirculated-air door is opened) *
- The coolant shut-off valve is closed *
- The valves of pump valve unit are closed and there is no
coolant circulation pump delivery *
- Compressor is actually driven (A/C Clutch -N25- operated,
overload safeguard (if installed) not tripped) *
Note
The A/C compressor is driven by different components
depending on the engine (belt or input shaft). The belt pulley
or the drive unit has an overload protection to protect these
components and the engine, if the A/C compressor is runs with
resistance. Refer to
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; A/C
Compressor (vehicle-specific repair manual).
Pressures, Checking
- Observe the test requirements. Refer to
→ Chapter "Test Requirements".
- Turn off the ignition.
- Connect the A/C service station. Refer to
→ Chapter "A/C Service Station, Connecting".
Vehicles with an electric operated valves in the refrigerant
circuit, which cannot be opened without power (for example the
Audi Q7 e-tron):
Note
On vehicles with high-voltage system and additional
functions of the A/C system ("heat pump operation" or "cooling
the high-voltage battery") valves may be installed in the
refrigerant circuit which cannot be opened without power. These
valves are opened and closed for example via a step motor and
after switching off the ignition are no longer activated. To
check the pressures in the refrigerant circuit with the A/C
system switched off no areas may be closed be closed, for this
reason the valves must be opened before these procedures. Refer
to
→ Heating, Ventilation and Air Conditioning; Rep.
Gr.87; Refrigerant Circuit; System Overview - Refrigerant
Circuit and the Vehicle Diagnostic Tester in the
"Guided Fault Finding" function.
- Open the electrically activated valves, which to now open
without power using the Vehicle Diagnostic Tester in the "Guided
Fault Finding" function.
All Vehicles
- Take the pressure gauge readings (two possible results):
- Pressure in refrigerant circuit lower than indicated in
table
- Pressure in refrigerant circuit in line with table or higher
Note
- Temperature of refrigerant circuit components should be
equal to ambient temperature. Pressure will deviate from values
in table if individual components of refrigerant circuit are
warmer or colder.
- At absolute pressure, 0 bar/psi corresponds to absolute
vacuum. Normal ambient pressure (positive pressure) corresponds
to 1 bar (14.5 psi) absolute pressure. 0 pressure corresponds to
an absolute pressure of 1 bar (14.5 psi) on most pressure gauges
(indicated by -1 bar (-14.5 psi) below 0).
- For vehicles with High Pressure Sensor -G65-, Refrigerant
Circuit Pressure Sensor -G805- or A/C Pressure/Temperature
Sensor -G395-, etc. for which measured pressure is displayed in
measured value block, pressure measured should coincide. Use the
Vehicle Diagnostic Tester ("OBD" or "Guided Fault Finding for
the A/C system") and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit (vehicle-specific
repair manual).
- Pressure is measured in different units: 1 MPa (145 psi)
corresponds to 10 bar (145 psi) positive pressure. 1 bar (14.5
psi) absolute pressure corresponds to 0 bar/psi positive
pressure and thus to the ambient pressure (atmospheric
pressure).
Pressure in refrigerant circuit lower than indicated in
table
Not enough refrigerant in refrigerant circuit
- Determine refrigerant circuit leaks. Refer to
→ Chapter "Refrigerant Circuit, Determining Leaks ".
- Check the pressure relief valve.
If pressure relief valve has responded:
- Check the coolant fan activation.
- Check the refrigerant lines and hoses for cross-section
constrictions caused by inadequate bending radii.
- Check the refrigerant lines and hoses for external damage.
- If no fault is found, clean the refrigerant circuit (flush
using refrigerant R134a. Refer to
→ Chapter "Refrigerant Circuit, Cleaning (Flushing), with
Refrigerant R134a"; or blow through using compressed
air and nitrogen. Refer to
→ Chapter "Refrigerant Circuit, Flushing with Compressed Air and
Nitrogen").
Pressure in refrigerant circuit in line with table or higher
- Start the engine or activate the ready mode (for example on
vehicles with a high-voltage system).
- Set the A/C system to maximum cooling output.
Note
- On vehicles with A/C Compressor Regulator Valve -N280-, the
control current can be read in the measured value block. Use the
Vehicle Diagnostic Tester (Function "OBD" or "Guided Fault
Finding" of the Air Conditioning) and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; A/C
Compressor (vehicle-specific repair manual).
- On vehicles with an Electrical A/C Compressor -V470- read
out the A/C Compressor Speed Sensor using the different control
modules (for example via the respective climate control module
or the Thermal Management Control Module -J1024-) using the
Vehicle Diagnostic Tester in the "Guided Fault Finding"
function.
Vehicles with a Mechanically Driven A/C Compressor
If A/C compressor is not driven with the engine running or
regulating valve is not actuated:
- Determine and eliminate cause, for example by checking A/C
system DTC memory.
- Observe the test conditions.
- Check the A/C Clutch -N25- voltage supply. If it is OK,
repair the A/C clutch.
- Check the A/C Compressor Regulator Valve -87- activation.
Use the Vehicle Diagnostic Tester (Function "OBD" or "Guided
Fault Finding" of the Air Conditioning) and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; A/C
Compressor (vehicle-specific repair manual).
Note
- If the low pressure switch was removed to connect the
service station, bridge the electrical connections in the
corresponding connector for the pressure measurement.
- A/C compressor is driven by the engine via A/C Clutch -N25-.
- The A/C Compressor Regulator Valve -N280- is activated by
the Front A/C Display Control Head -E87- or Climatronic Control
Module -J255-. Use the Vehicle Diagnostic Tester (Function "OBD"
or "Guided Fault Finding" of the Air Conditioning) and
→ Heating, Ventilation and Air Conditioning; Rep. Gr.87; System
Overview - Refrigerant Circuit (vehicle-specific
repair manual).
Vehicles with an Electrical A/C Compressor -V470- (Vehicles
with a High-Voltage System)
If the electrical A/C Compressor is not activated while the
ready mode is active:
- Check the activation of the A/C compressor via the
respective control module. Refer to
→ Heating, Ventilation and Air Conditioning; Rep.
Gr.87; Refrigerant Circuit; System Overview - Refrigerant
Circuit and use the Vehicle Diagnostic Tester in the
"Guided Fault Finding" function.
All Vehicles
- Checking pressures on vehicles with a restrictor and
reservoir (with internally regulated A/C compressor). Refer to
→ Chapter "Checking Pressures for Vehicles with Restrictor and
Reservoir (with Internally Regulated Compressor)".
- Checking pressures on vehicles with an expansion valve and
receiver/dryer (with internally regulated A/C compressor). Refer
to
→ Chapter "Checking Pressures on Vehicles with Expansion Valve
and Receiver/Dryer (with Internally Regulated Compressor)".
- Checking pressures for vehicles with restrictor, reservoir
and A/C Compressor Regulator Valve -N280- (externally regulated
A/C compressor). Refer to
→ Chapter "Vehicles with Restrictor, Reservoir and A/C
Compressor Regulator Valve -N280- (Externally Regulated A/C
Compressor), Checking Pressures".
- Checking pressures on vehicles with restrictor,
receiver/dryer and A/C Compressor Regulator Valve -N280-
(externally regulated compressor). Refer to
→ Chapter "Vehicles with Restrictor, Receiver/Dryer and A/C
Compressor Regulator Valve -N280-, Checking Pressures,
Externally Regulated Compressor".
- Check the pressures on vehicles with an electrically-driven
A/C compressor (Audi A3 e-tron, Audi Q5 hybrid, Audi Q7 e-tron
etc.). Refer to
→ Chapter "Checking Pressures on Vehicles with Electrically
Driven A/C Compressor (Vehicles with Hybrid Drive)".
READ NEXT:
General Information
Note
Connect the A/C service station. Refer to
→ Chapter "A/C Service Station, Connecting".
Observe the test requirements. Refer to
→ Chapter "Pressures,
General Information
Note
Connect the A/C service station. Refer to
→ Chapter "A/C Service Station, Connecting".
Observe the test requirements. Refer to
→ Chapter "Pressures,
Specified Values for the Refrigerant
Circuit Pressures
Note
Connect the Air Conditioning (A/C) service station. Refer to
→ Chapter "A/C Service Station, Connecting".
Observe the tes
SEE MORE:
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Mirror Trim
2 -
Bolt
1.5 Nm
3 -
Mirror Adjusting Unit
Removing and installing. Refer to
→ Chapter "Mirror Adjusting Unit, Removing and Installing".
4 -
Bolt
Tightening specification. Refer to
→
Overview - Suspension Strut and Upper Control Arm
1 - Bolt
Replace after removing
2 - Control Arm
3 - Shock Absorber Fork
Removing and installing. Refer to
→ Chapter "Shock Absorber Fork, Removing and Installing".
4 - Bolt
Replace after removi