ACC Control Module and Connected Components

Cars equipped with Automatic Climate Control (ACC) are different from cars equipped with A/C in that a number of sensors and actuator motors and an electronic control module have been added to the heating and ventilation system.

With the AUTO feature engaged, it is sufficient for the driver to give the desired cabin temperature between +17° C - +27° C (62.5 - 80.5° F) and the allow the ACC system to achieve and maintain the desired temperature in the car.
The system can also be manually controlled.

The ACC unit monitors temperature signals and signals from the solar sensor and controls the positions of the various dampers and the speed of the system and rear door fans in order to maintain the desired temperature in the car.

All sensors and control mechanisms are used by the ACC control module in order to maintain a comfort- able temperature by:
- Providing a reliable and comfortable temperature as soon as possible after the car is first started.
- Predicting changes due to varying conditions and carrying out the necessary adaptation as quickly and quietly as possible.

As electronics in general have developed quickly over the years, there have also been changes in the ACC control module. The software has been developed in order to achieve faster and more effective control of the temperature in the cabin.

The following has happened to ACC since 1985:

M1985
ACC generation 1. Registers solar intensity from the solar sensor and temperature readings from the outside air and cabin air as well as the mixed air (in heater housing). A number of diagnostic trouble codes can be read on the ACC panel display.

M1990
ACC generation 2. The control module flow also receives information about the angle of the sun in relation to the car. Other sensors are more accurate. The ACC control module is available in two versions, 2.00 with ROM 1 and version 2.01 with ROM 3. A scan tool (ISAT) can be connected, with which diagnostic trouble codes can be read and command codes can be entered into the control module. The ACC system can now also be calibrated so that the various dampers are correct in relationship to the desired position.

During the 90's, ACC generation 2 has been equipped with further diagnostic trouble codes and command codes and the control software has been improved over time.

Using drawings and pin numbers, the ACC section primarily describes M1995- and where there are large differences, these are dealt with.