The Heat is on
 

I just picked up a 1981 380SL. Everything works good except the climaite control. If I select auto hi or Auto low the fan speed changes but it only blows hot out of the defrost and the floor. nothing to the dash. Changing the temp wheel makes no difference. From what I have read it my be the mono valve. Do you have any other ideas and where is the mono valve (or other parts) located?

Very hard to diagnose CCU problems with the symptoms you have. It could be as easy as a vacuum element, vacuum switchover valve to the CCU unit itself needs replaced. The monovalve is easy to check - do a search "monovalve" and there is some great and extensive reading. Also in the DIY links and articles you will find some extensive CCU reading.

Thanks, I'll start with the monovalve and then check the vac.

My car had a similar issue where it would always blow hot air no matter what setting. The climate control fuse was blown. Check that first.

I'll look at that next. I found a blow up diagram for the heating and AC system and it shows the mono valve is only on 82s and forward. Some of the system seems to work. The air will switch from the defrost vents to bi level but not the dash vents. I also notice that the compressor does engage when on defrost or when the AC switch is on. I think it only blows out of the defrost and bilevel because it knows the air is hot. The question is what components control the flow of hot water on the 1981 models.

Thanks for the in put. http://www.peachparts.com/shopforum/...ons/icon14.gif

Fuses are OK
 

I checked the AC fuse and it looks OK. It's the same fuse for the blower motor and since the fan runs I'm sure its good. I still need to check the vac. Is there a way to check the servo or the ccu before swapping them out?