Heating Output and Temperature Door Activation, Checking, Basis

Heating Output and Temperature Door Activation, Checking, Basis

Test requirements are met, refer to => [ Heating Output and Temperature Door Activation, Testing Requirements ] Heating Output and Temperature Door Activation, Testing Requirements.

- Close the engine hood.

- Close the doors, the windows, the sunroof and the rear lid.

- Open all instrument panel vents.

- Turn on the ignition and activate the ready mode, the engine start by itself if needed (high voltage vehicles).

- Start the engine (not high voltage vehicles).

Set the Climatronic control module (J255) as follows:

• "Auto" operating mode (indicator light on the AUTO button lights up).

• Temperature preselect "cold" (display"LO" in the MMI display).

• The A/C compressor is on (the indicator lamp on the AC button comes on).

• Preselect for the fresh air blower "maximum speed" (in the MMI display, level "10" or greater).

• Set the vent direction using the rotary switch on the A/C Control Head to "footwell vents" and "instrument panel vents" (displayed in the Multi Media Interface display).

• The indicator lamp in the AUTO button goes out when the vent direction for the air or fresh air blower speed is manually changed.

• The maximum possible fresh air blower speed depends on several conditions (coolant temperature, vehicle voltage, etc.)

- Perform Guided Fault Finding on A/C system and select the "Read measuring value block" function using the Vehicle diagnostic tester in "Guided Fault Finding".

- Let the A/C run a few minutes with maximum cooling output (A/C compressor is switched on, indicator lamp in the AC button comes on).

- Compare the evaporator vent temperature sensor (G263) measured value to the measured values from the center outlet temperature sensor (G191) and the footwell vent temperature sensor (G192) ).

Target values:

• The center outlet temperature sensor (G191) and footwell outlet temperature sensor (G192) measured values may not be greater than maximum 5 °C (41 °F) after 5 minutes, than the evaporator vent temperature sensor (G263) measured value.

If the required values are not reached, perform a Fault Finding at a temperature increase on the evaporator

- Using a commercially available thermometer, measure the air temperature coming out of the instrument panel vents (left, right and center) and out of the front and rear footwells and compare the measured values with displayed measured values from the center outlet temperature sensor and the footwell outlet temperature sensor.

Target values:

• The measured values with the thermometer may be maximum 5 °C (41 °F) lower or higher than the measured values from the center outlet temperature sensor and the footwell outlet temperature sensor.

If the required values are not reached, perform a fault finding at a temperature increase on the evaporator

- Using the dial on the Climatronic control module, select the "Warm" ("Hi" in the MMI display).

- Using a commercially available thermometer, measure the air temperature coming out of the instrument panel vents (left, right and center) and out of the front and rear footwells and compare the measured values with displayed measured values from the center outlet temperature sensor and the footwell outlet temperature sensor.

Target values:

• The measured values from the center outlet temperature sensor and the footwell outlet temperature sensor in the display fields are greater than 52 °C (125 °F) (depending on the engine temperature at the time).

• The measured values (temperature of the air coming out of the vents), after 5 minutes, may be maximum 5 °C (41 °F) greater or smaller than the measured values from the center outlet temperature sensor and the footwell outlet temperature sensor.

• Depending on the engine, for example, on the 8 cylinder engine, it may be necessary to increase the engine from 1,200 to 1,500 to reach the required temperature. The heating performance of the engine or coolant flowing through the heater core may not be sufficient when the engine is running in idle to bring the necessary warming energy into the heater core (for example, on an 8 cylinder engine with an idle RPM of approximately 650).

• At the setting "Warm" the specified outflow temperature on the evaporator is controlled to approximately 10 °C (50 °F) by the Climatronic control module.

• On high voltage vehicles, lower the fresh air blower (V2) speed. The coolant pump (V50) delivery is not always enough to supply the required heat output when the engine is running and the fresh air blower is set to the highest setting.

If the specified values are not reached, check the following:

• Repeat the heating output at an engine RPM of approximately 1,500 to 2,000 (at a low fresh air blower speed on high voltage vehicles). If the heating performance is not reached at the engine RPM (fresh air blower speed), the fault is not with the A/C unit but rather inside the coolant circuit (a combination of the A/C system in the coolant circuit, engine coolant pump delivery, the coolant flowing through the heater core, etc. Refer to => [ Heater Core/Housings ] Heater Core/Housings ).

• Actuation and function of the temperature regulator door motor (V68) and the actuation of the temperature door (via the connecting rod), refer to => [ Heater Core Housing Temperature Doors ] Heater Core Housing Temperature Doors,=> [ Temperature Regulator Door Motor (V68) and Rear Temperature Door Motor (V137) ] Temperature Regulator Door Motor (V68) and Rear Temperature Door Motor (V137) and the Vehicle diagnostic tester in "Guided Fault Finding".

• Foam seal on heater core for heater of A/C unit, refer to => [ Heater Core Removing and Installing ] Heater Core Removing and Installing.

• Check the engine coolant pump for correct function (if the coolant pump is defective, it is possible that not enough coolant is flowing through the heater core for heating in the A/C unit).

• Coolant pump (V50) activation and function (if the coolant pump is faulty, then not enough coolant is flowing through the heater core in the air conditioner for heating). Refer to the Vehicle diagnostic tester in "Guided Fault Finding".

• The coolant pump (V50) maintains the coolant flow through the heater core heater in the A/C system when the engine is not running for vehicles with a start-stop system and for high voltage vehicles.

Temperature Increase Downstream from Evaporator, Determining Malfunction