Malfunction Determination - Cooling Output of Front A/C System OK But Required Values Not Achieved In Rear - Comfort System

Malfunction Determination - Cooling Output of Front A/C System OK but Required Values Not Achieved In Rear - Comfort System

• For testing the cooling output in the rear, the temperature of the air from the rear center console vents is measured with a thermometer.

• So that the rear temperature sensors ( Left rear upper body vent temperature sensor (G635) / Right rear upper body vent temperature sensor (G636) , Left rear footwell vent temperature sensor (G637) / Right rear footwell vent temperature sensor (G638) ) measure the correct temperature, sufficient air must be able to flow past. Change the air flow direction if necessary.

Requirement for this test:

• The cooling output of the A/C system was checked and is OK. Refer to => [ Cooling Output, Checking ] Cooling Output, Checking.

When testing the cooling output, it is helpful to display the following measured values of the rear A/C display control head (E265) :

• Measured values of the following temperature sensor: Left/right rear upper body vent temperature sensor (G635) / (G636) , left/right rear footwell vent temperature sensor (G637) / (G638).

- Open the vent in the left and right B-pillars

- Ensure that the air outlet from the rear footwell vents (under the front seats) is not blocked by floor mats or other objects.

- Set the air distribution on the rear A/C display control head so that the air is routed to all vents.

- Repeat the cooling output test and read out and record the measured value of the Evaporator vent temperature sensor (G263). Refer to => [ A/C Unit, Checking Cooling Output ] A/C Unit, Checking Cooling Output.

- In the "read measured values" function of the rear A/C display control head, select the display group with the measured values for the temperature sensors Left rear upper body vent temperature sensor/Right rear upper body vent temperature sensor, Left rear footwell vent temperature sensor/Right rear footwell vent temperature sensor using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

- Use a thermometer to measure the temperature of the air from the vents in the left and right rear center console (the measured values correspond to the temperatures previously measured by the evaporator vent temperature sensor (G263) , permissible deviation +9° C (48 °F). Refer to => [ Cooling Output, Checking ] Cooling Output, Checking).

- Pay attention to the measured values of the different temperature sensors during the cooling output test.

- Do the temperatures in the rear measured by the various temperature sensors correspond to the temperature of the air from the vents in the left and right rear center console measured by the thermometer (the permissible deviation of the displayed values from the temperature measured at the evaporator vent temperature sensor is less than +9°C, the measured values correspond approximately to the temperature measured with the thermometer)?

• Since the air cooled by the A/C unit must flow backward through the air guide channel under the center console, it may take some time for the air at the rear vents to reach the required values.

• If the required temperature is not achieved at a temperature sensor, change the setting at the rear A/C display control head so that more air flows past this temperature sensor.