Hi! Im new to this forum and I see there is a lot of guy with experience on the w123! Im the owner of a 1983 MB 300td. I have done a lot of search, found many other ACC related problems, troubleshooted my system, and dont know what to do now!

Here is my trouble! It is starting to be cold outside ( -1, 0, +1 C ) and I cant have hot air blowing in my car. Last month I had really hot air for the first 5 min drive, then it was turning to cold, and stayed cold for the rest of the ride, no mather wich button I press. Since the la 4-5 days, its just always cold air blowing.

My engine is heating good, always around 80 F, and I know I can have burning hot air inside when the system permit. I tought it was my control unit at first. I removed it, opened it and re-soldered every connection. Nothing changed. Then I tought it was the monovale, I disconnected it ( I think its supposed to be normally open/always hot) and ran the car like that. With no current going to the monovalve, I can get really hot air when the dial is set to COLD! If I dial it to hot, then its blowing to my face only cold air again.

Seems like something is giving a wrong signal to my monovalve?

Did some of you guys ran into something like that before?

Winter is coming ( -30 C ) and I would like to have some hot air