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.
-- Turn 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):
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, therefore the valves must be opened before this procedure. Refer to Refrigerant Circuit and use 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
| Ambient Temperature in °C (°F) | Pressure in Refrigerant Circuit in bar (psi) Positive Pressure |
|---|---|
| 15 (59) | 3.9 (57) |
| 20 (68) | 4.7 (68) |
| 25 (77) | 5.6 (81) |
| 30 (86) | 6.7 (97) |
| 35 (95) | 7.8 (113) |
| 40 (104) | 9.1 (132) |
| 45 (113) | 10.5 (152) |
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 Refrigerant Circuit .
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 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 REFRIGERANT CIRCUIT, CLEANING (FLUSHING) WITH REFRIGERANT R134A ; or blow through using compressed air and nitrogen. Refer to 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.
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 A/C Compressor .
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 A/C Compressor .
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 Refrigerant Circuit .
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 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 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 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 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 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 PRESSURES, CHECKING, VEHICLES WITH ELECTRICALLY DRIVEN A/C COMPRESSOR (VEHICLES WITH HIGH-VOLTAGE SYSTEM) .