Air Door: Testing and Inspection

General Information

Special tools, testers and auxiliary items required

• Vehicle Diagnostic Tester in the "Guided Fault Finding" function and the corresponding connection lines Workshop equipment.

• A standard thermometer (for temperature measurements, if necessary a thermometer with 2 measuring probes for simultaneous measurement for example for temperature on the right and left)

• In vehicles without a rear A/C unit (with a rear air distributor housing), the temperature of the air flowing from the front A/C unit to the rear air distributor housing is regulated by the Climatronic control module (J255) , so that an average temperature is set for the air from the vents in the front area. The target temperature for the air from the vents in the front area is calculated via the setting for the left and right side on the Climatronic control module by the Climatronic control module. However, if a setting which no longer regulates the temperature (for example HI for maximum heating or LO for maximum cooling) is present on the Climatronic control module, the temperature of the air from the vents in the front area is no longer regulated. If, for example, maximum heating HI is set on the Climatronic control module for one side and maximum cooling LO for the other side, the air for the vents in the front area is maximally heated.

• Certain A/C system functions can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"car systems" menu. The A/C system control can also be influenced via presettings in the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"car systems" menu. Therefore, first check the presetting in the MMI in the case of a problem with these components. Refer to Infotainment/MMI operating instructions.

If the coolant circuit is not completely bled after filling, air may accumulate in the heater core of the front A/C unit (and in the rear A/C unit if present), thus reducing the heating output of the A/C system. Additional noises may occur or the customer may complain of different air temperatures flowing out of the vents on the driver side and front passenger side (front and rear, left and right rear) at the same setting.

Corrective action:

- Check the coolant circuit and bleed it again if necessary, refer to => [ Coolant Circuit, Bleeding ] Coolant Circuit, Bleeding.

- If it is suspected that air remains in the cooling system after the bleeding operation. Perform a lengthy test drive at high engine speed (at least 10 minutes, engine speed above 2500 rpm). Select a low gear during the test to prevent excessive vehicle speed.

In the event of a customer complaint regarding poor heating output at certain engine speeds:

- Check the incorporation of the heater core in the front A/C unit (and in the rear A/C unit if present) into the coolant circuit. If, for example, the two coolant hoses (supply and return) of the engine are interchanged, the coolant is flowing in the wrong direction through the heater core. It is also possible for the coolant recirculation pump (V50) to be working against the coolant pump of the engine, refer to => [ Incorporation of A/C System in Coolant Circuit ] Incorporation of A/C System in Coolant Circuit.

If a different air temperature is coming out of the vents during A/C system control mode, it may be caused by the following.

• One or more temperature doors in the front A/C unit (or in the rear A/C unit if present) does not close completely or does not reach its end position.

• Air is in the heater core of the front A/C unit (or of the rear A/C unit). This results in fluctuating flows through the affected heater core and the heat is not distributed uniformly.

• A foam seal loosened during installation of the heater core and air can flow past the heater core, refer to => [ Heater Core With Front A/C Unit Installed ] Heater Core With Front A/C Unit Installed and => [ Rear Heater Core ] Rear Heater Core.

• The A/C system refrigerant circuit is not filled with the correct quantity of refrigerant (perform a cooling performance test), refer to => [ A/C Unit, Checking Cooling Output ] A/C Unit, Checking Cooling Output.

• A start-stop system is available as optional equipment for certain engines of this vehicle. Depending on the setting on the Climatronic control module (or if present at the rear A/C display control head (E265) ), it can prevent the stop function. If, for example, the defrost mode is selected on the Climatronic control module, the stop function is not possible or will be interrupted and the engine will start as soon as this operating mode is selected. The same applies in the case of heating and cooling. The difference between the target and actual temperature is greater than a specified value using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

• In vehicles with a start-stop system, the coolant recirculation pump (the recirculation pump (V55) of the parking heater) is activated even when the stop function is active in order to maintain the coolant flow through the heater core, refer to => [ Vehicle Rear and Luggage Compartment Components ] Vehicle Rear and Luggage Compartment Components, and Vehicle Diagnostic Tester in the "Guided Fault Finding" function.

Information For Vehicles With Auxiliary Heater

In the case of a complaint regarding poor or insufficient heating output in vehicles with a parking heater as optional equipment, check the activation and function of the heater coolant shut-off valve (N279) and the recirculation pump (V55) check using the Vehicle Diagnostic Tester in the "Guided Fault Finding" function (of the parking heater).

• Certain A/C system functions can be switched on and off via the MMI (Multi Media Interface) under the "A/C system" function in the "car"/"car systems" menu. Among other things, the activation of the auxiliary heater installed in vehicles with a diesel engine can be switched off. Therefore, first check the presetting in the MMI in the case of a complaint regarding poor heating output. Refer to Infotainment/MMI operating instructions.

• Heating output and temperature door activation, testing requirements, refer to => [ Heating Output and Temperature Door Activation, Testing Requirements ] Heating Output and Temperature Door Activation, Testing Requirements

• Heat output and temperature door activation, checking, refer to => [ Heat Output and Temperature Door Activation Tests ] Heat Output and Temperature Door Activation Tests

• Check the activation of the auxiliary air heater (for vehicles with TDI, refer to => [ Auxiliary Electric Heater (Z35) ] Description and Operation.