Hi folks;
Whenever you have the symptom heat at idle and low speed and then no heat at >1500rpm and hwy speed you are most likely suffering from having a mono valve that either has gone bad or you have a cheap replacement insert installed in it. The $15 replacement inserts WILL NOT work - their internal spring rating is incorrect. Aux pump and high engine speed will literally "suck" the valve seat into the closed position no matter the temp wheel setting and voltage on the mono valve. You HAVE to get the genuine part 000-835-06-44 (Peachparts shows it, but it appears to be out of inventory). The cheap repair inserts will drive you absolutely insane and you will only have heat traffic lights.

What about if your temperature wheel is in the cold/blue "min" setting and you get low amounts of heat, sometimes high heat? It never did that before, it just starting doing that.

My indy replaced the monovalve, ACC switch and aux water pump. Still no heat for about 20 min, if I turn the car off then on, I get heat for about 10 min. Do I have a vacuum leak? The floor vents are not working.

What year/model?

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )