Please help with climate control
 

I have a 1983 300 sd and it burns the traces in the climate control unit if I turn on the fan motor. I have put in two units and it smoked them both. What do I need to check first, It has a new blower motor. I have nothing to go by but I am a technician if someone can point me in the right direction.I just bought the car and really like it other than this problem Thanks

Which climate control unit are you referring to?
There are three modules: push button assembly, electronic unit for blower speed control, electronic unit for temperature control.

Trace the circuit path on the printed circuit to see which pin it goes to on the connector.

If it is the pushbutton assembly, a common problem is a seized auxiliary water pump that burns traces.

Welcome to the world of MB ACC. There are many posts for this issue if you use the search. Also the factory service manual will be most helpful. The online link is here also. http://mb.braingears.com/ Study the wiring diagram for the ACC, and then start tracing leads. I also agree with Rick76 on the seized aux. electric water pump. It is there so you get sufficient water flow when the engine is running low RPMs. Most people put a 1 amp inline fuse to this pump so it won't fry the board again. It is a complicated system but it is just a matter of diagnoses and testing components.

Thanks to both of you for your reply . I will check out and let you know the results.:)

Once again I want to thank both of you for responding. I went to the auxillary water pump and it was locked up. Iunplugged it and resolderd the board and it has been working great. Thanks so much for your help.:)