fiskarflugen

Bought a used 1991 C2 that is in rough shape. None of the CCU controls, ie fan, AC, vent switch, etc appear to work. I checked the rear blower relay and fuse. Is there a simple way to check if the CCU is bad using a multi-meter??

springer3

You can check almost anything electrical with a multimeter, but you need the chassis wiring diagram, and you need to check the items connected to the CCU. The CCU reports fault codes to the diagnostic system, so if you can get a code reader, it will tell you if the CCU is at least still talking.

I have some success fixing CCUs on similar vintage Mercedes, but my 964 has caused no problems and therefore I have no experience there. Mercedes uses a similar CCU, and most of the time the problems are either accessory failures (actuators), or cold solder joints.

Read the codes first. If that does not help, pull the unit, and check the items connected to the CCU. Then open the CCU and get a good magnifying glass or, even better, a microscope and look at the solder joints. A bad joint is tricky to spot, so it would help to have someone with experience show you. A good solder joint looks uniformly glossy and smooth. Sometimes a cold joint looks normal until you get some magnification.

Good luck.

KirkF

Nothing beats having a Bosch hammer for this task. It can read the codes from the CCU, and it can read and operate all of the sensors and motors related to the CCU.

Kirk