Climate Control/Blower Regulator Help

[IanJ]

I'm trying to diagnose what I believe is multiple problems with the climate control on a '85 300D that I recently acquired. When I got the car the climate control was all screwed up. The blower would run when climate control was set to off, but only on high speed... and turn off when on EC....otherwise always in defrost mode. I pulled the climate control unit and found a circuit in it to be burnt/broken. I carfully soldered a jumper over the burnt circuit, but when I plugged it in another circuit started smoking and burnt through. I have a replacement control unit now, but I'm afraid to plug it in until I'm sure some other problems aren't frying the control unit.

While searching for wiring problems I found that the blower regulator was cracked and partially out of the housing.

Is there a way to test the blower regulator? (anybody have a used one?)
Any ideas what could fry a climate control unit or is this likely caused by an internal short in the unit?

Sorry about the long post... but any help would be appreciated.