It is possible the wires are hooked up backwards but I doubt it. I had many many problems with my climate control unit before I finally got it fixed. So many I won't list them all. I heard ALL of the reasons and still nothing improved. The control panel was replaced twice, numerous thermostats were replaced many times, vacuum system was hauled apart once and still the climate control system would not work correctly. All warrenty work. Then the compressor etc stopped at 51000 miles and I got the bill. MB helped with part of it but not much. Since the warrenty is out I now go to a local independent.

A local mechanic fixed the problem on the first try. Have your car checked for error codes. If you have lots of error codes, some of which are not related to the climate control unit. there is a relay in the car that is bad. I can not remember which one it is but it was expensive, sorry. That was money well spent as the climate control has been perfect ever since. The best part of this story is that I made a new friend and will always take my car to Chuck for repairs I can't do or are too lazy to do.

Have a great day

Paul
1999 E300D
87000