C) Control Unit/Flap Function

C) CONTROL UNIT/FLAP FUNCTION

The control unit is mounted on the left side of the air box and has two electric plug connections (S1 and S2).

The control unit comprises an electronic control for activation of the solenoid valves and a motor for operation of the temperature control flaps.

The control unit can be checked with a the control switch or a simple (locally made) tester.

1. Operating Motor Test

Turn on ignition and set program lever optionally to ECO, AUTOM. or BI position. The temperature selection lever has a microswitch in each of both final positions (18 °C and 30 °C), which is closed in these positions and shorts the regulating potentiometer. This means that the air conditioner switches to max. cooling in the 18 °C position or max. heating in the 30 °C position. The operating motor of the control unit must be running in its lowest position (cooling) in the 18 °C position or highest position (heating) in the 30 °C position.

The position of the temperature control flaps can be checked through the center nozzle duct in the heating position. They must be opened fully.

If the operating motor does not run, check the voltage on terminals 3 and 11 of plug (S2) - sensor system is okay - then replace the control unit.

Note: The microswitch of the 30 °C position (max. heating) is standard only since about 7/80.

2. Solenoid Valve Activation Test (Test Lamp)

It is recommended to remove the control switch and trim panels on the sides of the center console (see B 4a), to be able to check the activation of solenoid valves.

Connect test lamp on car ground (never use the solenoid valve holding bar). Place test tip on each electric wire connection.

Note:
The cold start interlock must be switched off.
Coolant temperature above 40 °C.
This temperature is guaranteed, if the needle of the coolant temperature gage has reached the end of the first white section.
Valves are arranged with 180° displacement since 1983 models. It is recommended to remove the entire center console for testing.

Set center nozzle switch to up (open), pull off plug Si on control unit and turn on ignition. Set temperature control lever to 18 °C.

A) Testing Switch Contacts in Control Switch Program Selection Switch

Connect test lamp between body ground and valve being tested.




B) Testing Switch Contacts in Control Unit (Operating Motor)

Connect plug S1, set center nozzle switch to up (open) and turn on ignition. Connect test lamp between body ground and valve being tested.




C) Testing Control Unit (Operating Motor) Function (Temperature Control Switch Set To 18 °C)

Connect test lamp on body ground and terminal ... of plug S1 (S2). Turn on ignition. Test lamp should come on.




Check wire connections (see wiring diagram), if there is no activation in the one or other case. If the control switch or control unit has a fault, these parts must be replaced.

3. Flap Function

The vacuum units used to regulate the flaps are activated by the solenoid valves. The flap regulation can be checked together with the above mentioned test. The pertinent flap must be in the following position when the test lamp lights up on a certain valve and vacuum is available.