No heat with evil servo
 

I have not been able to get heat in my 1980 300sd with the dreaded evil servo setup. The original servo in the car was not working, severely cracked and plugged up with crud. I recently replaced it with a nice used aluminum unit. The motor in the new servo seems to work because I can hear it running after I shut the car off. I also replaced the amplifier with a rebuilt unit and put in a new auxilliary water pump which is working. When I push the defrost button, the blower comes on but I get no heat. When I push auto lo or auto high, the blower will not come on at all. So i have two questions. Number one, why am I not getting any heat in defrost? Number two, why will the blower not even come on in the auto lo or auto high positions?

It works in the defrost position because that is the default for the system. I linked the manual for the evil servo system in a post here so if you search on my username and servo manual, you'll find a link.
There is a central vacuum control switch which has to be activated for the system to function but if your blower is working, I believe that switch is functional. On my W116 there appears to be a second main switch next to the main vacuum switch. I've never looked into it far enough to determine what that switch controls but maybe it's not working correctly. On the W116 the vacuum control switch and the other switch are behind the glovebox.

Answer
 

Servo service manual
http://www.peachparts.com/shopforum/general-information/240606-evil-servo-service-manual.html#post2053754


http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm









Have a great day.