1981 380SL/SLC Climate Control

[Mike1953]

OK... Same problems, different twist...
81 mercedes was purchased in summer 2011 (in Houston, Texas) in great shape with a new updated air conditioning system. The air con system works great! Then weather got cold. No heat. Got the usual dialog and have read all of the blogs about how problematic this system is, etc...

One mechanic says SERVO looks good, I need a new climate control panel in the car. Bought that on ebay and changed it out... No heat! Everybody points their finger at the SERVO. One mechanic has me do the "turn the ignition switch to acc and turn on Defrost and listen to the SERVO - still no noise ... You need a new SERVO!"

Bought a new SERVO and installed it... Still no heat! Whats worse "turn the ignition switch to acc and turn on Defrost and listen to the SERVO - still no noise"...

It's freezing outside; temperature gauge set at 85F; car on; system comes on and blows ambient air; also center vents not blowing air. I can prop the vent open (through the center vent) - it's not broken, looks OK. Also appeared to cycle open and closed on me when I first started the car. I know there is this whole thing about a vacuum leak, and It is possible that I wind up pulling the gloove box/dash and start troublshooting vacuum leak/looking at vacuum/pods, etc.

But I still believe that if the SERVO was delivery hot water to the heater box, I would be getting some indication of warmth inside the vehicle - but nothing! I'm just not convinced that this is happening.

Hot water pump (mounted between the SERVO and the overflow tank) not working?
No power to the SERVO?
SERVO amplifier hosed?
A short in the electrical to the SERVO?
Something else?
Anything else?
Everything else?

I also understand that I could be looking at a number of problems, but I have gotten to the point that I don't no where to look. Also it is possible new air cond installation mechanic defeated heater because there was some problem. There seems to be an "it's OK to defeat features and live with it" culture on this car. Have had a number of mechanics suggest I forget about it and park the car in the winter. Me? I want to fix the problem.

Can anybody coach me here?