Ventilation System Heat Output And Pump Valve Unit Function, Checking

• If the coolant circuit is not completely bled after filling, air may accumulate in heat exchanger of the A/C unit, thus reducing heating performance of the air conditioner, additional noises may occur, or the customer may complain of different air temperatures flowing out of vents at the driver side and front passenger side despite an identical setting. Refer to COOLING SYSTEM, DRAINING AND FILLING .
• Under certain ambient conditions, if there are complaints of odd noises from the heat exchanger or poor heat output from the A/C system (an error may be stored at the coolant pump -V50- Check the pump/valve unit connection in the coolant circuit. If air bubbles are visible in the upper connection of the coolant expansion tank while the engine is running, also check the coolant expansion tank to ensure it is the correct version.

Corrective action:

• At the Climatronic Control Module -J255- A/C control head, set the A/C system to maximum heat output (temperature preset to Hi or both temperature preset rotary switches turned to the right stop) for the driver and passenger sides.
• Perform a lengthy test drive at high engine speed (at least 10 minutes, engine speed above 2500 rpm). If necessary, select a lower gear to prevent excessive vehicle speed.
• In the event of customer complaints about poor heating output at certain engine speeds, check incorporation of pump/valve unit into coolant circuit. If both coolant hoses (supply and return) from the engine to the pump/valve unit, or the electrical pins in the connector for the coolant pump -V50- have been interchanged, the engine coolant pump works in opposition to the pump in the pump/valve unit, and at certain engine speeds coolant no longer flows into the heat exchanger. and refer to the appropriate Wiring Diagram.

Pump Valve Unit, Checking Function

In this test, function of pump valve unit (left heat regulating valve -N175-, right heat regulating valve -N176- and coolant pump -V50-) is checked.

• If the determined temperatures lie below the specification (heating performance too low):

-- If necessary, check the function of the pump/valve unit (-N175-, -N176- and the -V50-) in the Guided Fault Finding function using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.

If no malfunctions are detected:

-- Check for transposed or constricted coolant hoses (from the engine to pump/valve unit or from the pump/valve unit to the heat exchanger of the A/C unit). .

-- Check for interchanged electrical terminals of coolant pump -V50- of pump valve unit (direction of pump operation). refer to the approriate Wiring Diagram.

Test requirements:

• Coolant circuit has been bled according to specifications. .
• All air ducts, covers and seals OK and properly fitted.
• The air flow through the dust and pollen filter is not obstructed by dirt. Refer to DUST AND POLLEN FILTER .
• Engine is warm.
• The vehicle battery (Battery -A-) is OK and adequately charged (to prevent the energy management control module -J644- from switching the Climatronic Control Module -J255- A/C control head off during the test).
• The DTC memory of the Climatronic Control Module -J255- A/C control head was checked and erased, basic setting was performed and the coding of the Climatronic Control Module -J255- A/C control head was checked in the Guided Fault Finding function using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.
• The Climatronic Control Module -J255- A/C control head adaptation has been checked using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.
• Vehicle not exposed to sunlight.

Checking

Test requirements are met.

Special tools and workshop equipment required 

• Diagnostic Operation SystemVAS 5051 (or Vehicle Diagnosis and Service SystemVAS 5052)
• Battery ChargerVAS 5900

-- Close hood.

-- Close doors, windows and sunroof.

-- Start engine and let it run a few minutes at maximum cooling performance (compressor is switched on, temperature preselect Lo for the driver and front passenger sides or both temperature preselect rotary switches are turned to the left stop).

-- Switch off ignition.

-- Connect the Battery ChargerVAS 5900 to the vehicle (so that the battery -A- is not excessively discharged. ).

-- With the ignition switched off, connect the Vehicle Diagnosis, Testing and Information SystemVAS 5051 with the Diagnostic Cable VAS 5051/5A to the 16-pin data link connector on the vehicle using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.

-- Switch ignition on.

-- Select the A/C-heating electronics in the Guided Fault Finding function using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.

The Climatronic Control Module -J255- A/C control head starts operation, the coolant pump -V50- is not actuated and does not run, left heat regulation valve -N175- and right heat regulation valve -N176- are activated and are closed).

-- Read the measured value block. There must not be any deactivations from the energy management control module -J644- in the Guided Fault Finding function using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.

-- Read the measured value block with the measured values for the left vent temperature sensor -G150- and right vent temperature sensor -G151- in the Guided Fault Finding function using the Vehicle Diagnostic, Testing and Information SystemVAS 5051.

-- Check the display with the measured values for -G150- and -G151-.

• Specification: Ambient temperature plus max. 15° C (59° F).

-- At the Climatronic Control Module -J255- A/C control head, set the temperature preset for the driver side to maximum heat output (temperature preset to Hi or the left temperature preset rotary switch turned to the right stop).

-- Read the measured value of the -G150- (the temperature value increases).

• Specification: approximately engine temperature (operation of coolant pump -V50-, left heat regulating valve -N175- open).

-- Read the measured value of the -G151- (the temperature value remains almost constant).

• Temperature increase less than 15° C (59° F) (right heat regulating valve -N176- closed).

-- At the Climatronic Control Module -J255- A/C control head, set the temperature preset for the passenger side to maximum heat output (temperature preset to Hi or the right temperature preset rotary switch turned to the right stop).

-- Read the measured value of the -G151- (the temperature value increases).

• Specification: approximately engine temperature (operation of coolant pump -V50-, left heat regulating valve -N175- and right heat regulating valve -N176- open).

-- At the Climatronic Control Module -J255- A/C control head, set the temperature preset for the driver and passenger side to cold (no heat output, temperature preset to Lo or both temperature preset rotary switches turned to the left stop).

-- Read out the display with the measured values for -G150- and -G151-.

• Specified Values Temperature drops within five minutes to the ambient temperature Ambient temperature plus max. 15° C (59° F) (operation of coolant pump -V50- does not run, left heat regulation valve -N175- and right heat regulation valve -N176- are closed).