Pressures, Checking
- Observe the test requirements. Refer to TEST REQUIREMENTS .
-- On vehicles with a high-voltage system, switch off (deactivate) the "auxiliary climate control" function. Refer to the Owner's Manual and Infotainment/MMI Operating Manual.
-- Switch off the ignition.
-- Connect the A/C service station. Refer to 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):
For vehicles with a high-voltage system and additional A/C system functions ("heat pump operation" or "cooling the high-voltage battery"), valves may be installed in the refrigerant circuit that cannot be opened without current. These valves are opened and closed via stepper motors, for example, and are no longer activated after switching off the ignition. To check the pressures in the refrigerant circuit with the A/C system switched off, no areas may be closed, therefore the valves must be opened before this procedure. Refer to Refrigerant Circuit (vehicle-specific service information) and use the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.
-- Open the electrically activated valves (not open without current) 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
| Ambient temperature (in degrees Celsius) | Pressure in refrigerant circuit in bar positive pressure |
|---|---|
| +15 °C (59 °F) | 3.9 |
| +20 °C (68 °F) | 4.7 |
| +25 °C (77 °F) | 5.6 |
| +30 °C (86 °F) | 6.7 |
| +35 °C (95 °F) | 7.8 |
| +40 °C (104 °F) | 9.1 |
| +45 °C (113 °F) | 10.5 |
The temperature of the refrigerant circuit components should be equal to the ambient temperature. Pressure will deviate from the values in table if individual components of the refrigerant circuit are warmer or colder.
At absolute pressure, 0 bar (0 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 one bar on most pressure gauges (indicated by -1 bar (-14.5 psi) below 0).
For vehicles with a High Pressure Sensor -G65-, Refrigerant Circuit Pressure Sensor -G805- or A/C Pressure/Temperature Sensor -G395- etc., for which the measured pressure is displayed in measured value block, the measured pressure should match the values in the table. Use the Vehicle Diagnostic Tester ("OBD" function or "Guided Fault Finding " for the A/C system). Refer to Refrigerant Circuit (vehicle-specific service information).
Pressure is measured in different units: 1 MPa (mega Pascal) corresponds to 10 bar (145.04 psi) positive pressure or 145 psi. 1 bar (14.5 psi) absolute pressure corresponds to 0 bar (0 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 REFRIGERANT CIRCUIT, DETERMINING LEAKS .
-- Check the pressure relief valve.
If pressure relief valve has responded:
-- Check the radiator fan activation.
-- Check the refrigerant pipes and hoses for cross-section constrictions caused by inadequate bending radii.
-- Check the refrigerant pipes and hoses for external damage.
-- If no error is detected, clean the refrigerant circuit (by flushing with refrigerant R134a, refer to Refer to REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or clean using compressed air and nitrogen, refer to REFRIGERANT CIRCUIT, CLEANING 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.
For vehicles with A/C Compressor Regulator Valve -N280-, the control current can be read in the measured value block using the Vehicle Diagnostic Tester (Function "OBD" or "Guided Fault Finding" of the A/C system). Refer to A/C Compressor (vehicle-specific service information).
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 requirements.
-- Check the A/C Clutch -N25- voltage supply. If it is OK, repair the A/C clutch.
-- Check the A/C Compressor Regulator Valve -N280- activation using the Vehicle Diagnostic Tester ("OBD" function or "Guided Fault Finding" for the air conditioning). Refer to A/C Compressor (vehicle-specific service information).
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 ("OBD" function or "Guided Fault Finding" for the A/C system). Refer to Refrigerant Circuit (vehicle-specific service information).
Vehicles with an Electrical A/C Compressor -V470- (vehicles with a high-voltage system)
If the electrical A/C compressor is not activated while ready mode is active:
-- Check the A/C compressor activation via the respective control module. Refer to Refrigerant Circuit (vehicle-specific service information) 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 Refer to PRESSURES, CHECKING, VEHICLES WITH RESTRICTOR AND RESERVOIR, INTERNALLY REGULATED A/C COMPRESSOR .
- Checking pressures on vehicles with an expansion valve and receiver/dryer (with internally regulated A/C compressor). Refer to Refer to PRESSURES, CHECKING, VEHICLES WITH EXPANSION VALVE AND RECEIVER/DRYER, INTERNALLY REGULATED A/C COMPRESSOR .
- Checking pressures for vehicles with restrictor, reservoir and A/C Compressor Regulator Valve -N280- (externally regulated A/C compressor). Refer to PRESSURES, CHECKING, VEHICLES WITH RESTRICTOR, RESERVOIR AND A/C Compressor Regulator Valve -N280-, EXTERNALLY REGULATED A/C COMPRESSOR .
- Checking pressures on vehicles with restrictor, receiver/dryer and A/C Compressor Regulator Valve -N280- (externally regulated compressor). Refer to PRESSURES, CHECKING, VEHICLES WITH EXPANSION VALVE, RECEIVER/DRYER AND A/C Compressor Regulator Valve -N280-, 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 Refer to PRESSURES, CHECKING, VEHICLES WITH ELECTRICALLY DRIVEN A/C COMPRESSOR (VEHICLES WITH HIGH-VOLTAGE SYSTEM) .