heat when stopped, not while driving
 

i cant get heat to work in my 84 diesel four door when i am completly stopped. some times i have to turn the dial to make it work. but it allways works when stopped. my problem is it wont work at all when im driving. it doesnt seem that the aux pump or the heat valve by the fire wall function when i am driving. but they do when i am parked. the heater has worked a few times while driving, but 95% of the time i get no heat while driving. only while the car is completly stopped. i can get lots of heat while at a stop light. but as soon as i start rolling the heat stops working. is there a vaccum leak? please help

The monovalve diaphragm is torn, replace it with the repair kit available online and it will fix the issue. The repair is very easy. Do a search for monovalve diaphragm and you will find a lot of info on the issue.

Welcome to the forums!

thanks for the answer pawo. but wouldnt i get heat all the time if the mono valve was torn. wouldnt it pass hot water all the time. when i am parked i can hear the aus pump running and i can make the mono valve turn on and off by disconnecting its connection. but as soon as i start driving every thing shuts down. do you still think its the valve? thanks for your time

If the diaphragm is torn the coolant will get past the valve and will not go into the heater core (when engine is at higher rpms) at low rpms it will drift into the core, providing some heat. You don't need to replace the whole monovalve, just get a "repair kit" from fastlane (Buy Parts) at the top of the screen. It will fix the problem. The part you need looks like this:

[IMG]http://www.***************/secure/PartImages/1147213007.jpg[/IMG]

thanks for all the info. i will take it apart and inspect. this is a great site. no one else around here works on mercedes. and the manuals i have dont trouble shoot. you have been very helpful. happy new year :)