Test Requirements

All Vehicles

• Checking the cooling output. Refer to the appropriate service information (vehicle-specific Service Information).
• Connections with valve and service connections for measurement and testing. Refer to Refrigerant Circuit (vehicle-specific Service Information).
• Connect the A/C Service Station. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .

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- or 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 and refer to the appropriate service information v (vehicle-specific Service Information).

-- 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 bars) 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 shut-off valves in the refrigerant circuit check the function and activation of these valves. Use the Vehicle Diagnostic Tester in the"Guided Fault Finding"  function for the A/C system. Refer to Refrigerant Circuit (vehicle-specific Service Information) and the appropriate service information (vehicle-specific Service Information).

-- 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 (vehicle-specific Service Information).

-- Discharge the refrigerant circuit, replace each reservoir/receiver/dryer with dryer or the dryer cartridge, and then evacuate the refrigerant circuit for at least three hours. Refer to Refrigerant Circuit (vehicle-specific Service Information) and WORKING WITH A/C SERVICE STATION .

Test Requirements

• Pay attention to the general information for checking the refrigerant circuit pressure. Refer to GENERAL INFORMATION FOR CHECKING THE REFRIGERANT CIRCUIT PRESSURE .

General test requirements (these only have an influence on the pressure gauge display for this measurement with the A/C system switched on)

• 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.*
• The drive unit for the A/C compressor is OK and installed correctly. *
• All air ducts, covers and seals are OK and properly installed *.
• The A/C system diagnostic does not detect any malfunctions (when the engine is running and the A/C system is switched on), and no compressor shut-off condition is displayed in the measured values (only for vehicles with "A/C system" diagnostic). Use the Vehicle Diagnostic Tester in the"Guided Fault Finding"  function for the A/C system.
• Air flow through dust and pollen filter not obstructed by dirt *.
• All instrument panel vents are open *.

Additional test requirements (these have an influence on the display of the pressure gauge on this measurement)

• Vehicle is not exposed to direct sunlight. Refer to the appropriate service information (vehicle-specific Service Information).
• The ambient temperature is greater than 15 °C (59 °F).
• The ignition is switched off.
• The A/C Service Station in connected to the refrigerant circuit. Refer to A/C SERVICE STATION ON REFRIGERANT CIRCUIT, CONNECTING .

• Refer to MECHANICALLY DRIVEN A/C COMPRESSOR, CHECKING PRESSURE WITH A/C SYSTEM SWITCHED ON .
• Refer to ELECTRICALLY-DRIVEN A/C COMPRESSOR, CHECKING PRESSURE WITH A/C SYSTEM SWITCHED ON