A/C - Control Module/Control Functions/Diagnostics

Date: April 4, 2008

Order No.: S-B-83.00/116

Supercedes:

Group: 83

SUBJECT:
All 164, 171, 203, 204, 209, 211, 215, 216, 219, 220, 221, 230 and 251 Vehicles

AC Control Module / Control Functions

If you receive customer reports in the above model vehicles of the below conditions, replacing the AC control module does not rectify the problem.

1. Air conditioning not functioning:

The sensors or actuators of the climate control system that are networked to the AC bus (e.g. sun sensors or actuator motors) can completely disable the AC bus if they are not operating. Please check the sensors, actuator motors and SDS for fault codes. If communication faults are stored, then the operating unit is not the cause.

2. Implausible control:

The multi-zone sun sensors have a significant influence on the temperature control. The sun shining at a specific angle can result in different outlet air temperatures and blower output on different sides of the vehicle. This effect is also possible on a cloudy day because of UV radiation. Adjustment of the interior temperature is also heavily influenced by environmental conditions (e.g. heat from the transmission tunnel, heat from the radio or COMAND unit influencing the in car temperature sensors). Replacing the operating unit will not change the control response.

3. Poor control quality/cold feeling, too warm, too cold:

Condition may be due to body leaks and predominantly occurs at high speeds. At very high speeds, the refrigerant compressor output is lowered to provide the engine with extra power; this can cause the report of "blower output too warm". Since this is a normal function, replacing the AC control module is not a solution. The same condition can occur during rapid speed changes (heavy braking, rapid acceleration).

4. Fogged windows:

This condition is not related to the operating unit. Possible causes include moisture in the vehicle interior, driving with the air conditioning off or with the air condition and recirculation mode on.

Perform the following if a report regarding one of the above conditions is received:

1. Check all steps in the diagnosis tree found on Star TekInfo --> EDAC --> Non EDAC Guides --> Vehicle Heating, Ventilation, and Air Conditioning (HVAC) Manual.

2. Erase the fault memory.

3. Perform system reset via circuit 30.

Note:
The operating unit is generally not the cause of reported concerns regarding climate control operation. Check all of the other components in the climate control system using the diagnostic tree prior to performing work on the operating unit. Always submit the related diagnosis printouts and findings report when submitting a warranty claim.