I'm having a problem with my Climate Control in my 1987 300D Turbo. The climate control blows hot air only when the wheel is turned to max hot, and at this point it is really HOT. At any other position its the coldest air possible that begins to blow. So I have to switch it on and off every few minutes. I decided that I will buy a used pushbutton unit, so I interchanged it with the unit from my 1990 300D 2.5 Turbo, to see it any other unit will work, or if it has to be the same model #. This worked great, I can regulate the heat and enjoy my ride.

If anyone can tell me if these units are interchangable, I don't wana buy a unit and find out in the summer that the a/c does not function becase of a different layout. Can anyone direct me to a Electronic Layout of these control units. I noticed that my '87 connection do not have a wire for pin #1 & pin #11 on the Right side plug in comparison with my '90 which does have one.

Second issue is in both vehicle's the hot air is much cooler when when I'm stopped at a red light. As soon as I begin drving, the air begins to blow significantly hotter. Someone told me this is some sort of Auxillary Pump??

ALL the help is appreciated. Thanks.