General Information For Checking The Refrigerant Circuit Pressure
Working on the refrigerant circuit with the A/C service station can normally be performed without needing to de-energize the high-voltage system.
Vehicles with Electric Operated Valves in the Refrigerant Circuit, Which Cannot Be Opened without Power:
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
Risk of damaging the A/C compressor or the A/C service station.
A short circuit between the high and low pressure side is possible when opening the valves with the A/C system is on.
- Never open the valves in the high or low pressure side when the A/C system is on.
The specific test requirements are vehicle-specific and described in the Service Information for the vehicle. Refer to COOLING OUTPUT, CHECKING .
Checking the cooling output. Refer to COOLING OUTPUT, CHECKING .
Connections with valve and service connections for measurement and testing. Refer to Refrigerant Circuit .
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 reduces, the expansion valve opens and the refrigerant can flow to the low pressure side.
Under certain operating conditions, residual moisture in refrigerant circuit can lead to an ice build-up at compressor regulator valve. This ice build-up interferes with A/C compressor regulation. The 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 vehicle and after a short time, A/C function is OK again.
- After a long drive, the vehicle windows fog up from the inside, vehicle windows are also not cleared by then pressing the Defrost button, after switching off the vehicle (or switching off the A/C system) and after a short time, A/C system function is OK again.
Corrective Measure:
-- On vehicles with an A/C 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"). If the sensor measured value is too low under the operating conditions described by the customer (at an ambient temperature above 0 °C (32 °F), longer when it is lower than 0 °C (32 °F) although the A/C Compressor Regulator Valve -N280- is not currently activated) or too high (above 10 °C (50 °F) even though the A/C system is working correctly). Can freeze-up due to incorrect activation of the A/C Compressor Regulator Valve -N280- of the incorrect measured value of the Evaporator Vent Temperature Sensor -G263-. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function of the A/C system. Refer to COOLING OUTPUT, CHECKING .
-- If the vehicle does not have an Evaporator Vent Temperature Sensor -G263-, check the vent temperature via, for example, the Footwell Vent Temperature Sensor -G192- at the "Lo temperature" or "cold" for the driver and passenger side, lowest setting (4 or 5 bar (58 to 72.5 psi)) for fresh air blower speed, air outlet in footwell and fresh air operation under operating conditions specified by customer. If the measured value of the sensor is too low (at an ambient temperature over 0 °C (32 °F), over a longer time colder than 0 °C (32 °F)) the evaporator can freeze-up due to the incorrect measured value. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding" function.
-- On vehicles with a shut-off valve in the refrigerant circuit, check the function and activation of these valves. Use the Vehicle Diagnostic Tester in the A/C system"Guided Fault Finding" function. Refer to Refrigerant Circuit .
-- With the engine running, check the refrigerant line from the evaporator (or from the inner heat exchanger) to the A/C compressor (thick pipe, low pressure side). 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. Refer to Refrigerant Circuit .
-- Discharge the refrigerant circuit, replace the receiver/dryer with dryer, replace and seal the reservoir with dryer or the dryer cartridge, and evacuate the refrigerant circuit for at least three hours. Refer to Refrigerant Circuit and WORKING WITH A/C SERVICE STATION .