Regarding a '79 300SD W116, with a fairly new climate control servo, and a newly working aux. water pump. My heat is amazing, well at first, then I start to sweat. My dial does not change the temp in the car. What part should I look at to resolve this? Any suggestions for repair would be appreciated.

I had the same problem with my '85 and the whole mono valve had to be replaced, not just the "insert". I'm not sure if you have this control valve, but I tried a new controller first also.

Thanks dan for the reply. My car has a climate control servo rather than a monovalve and it is new so I don't think it is that. I appreciate the input.