I have a 91 560 SEL. My heating issue is very weird. When using any button the heat produced is minimal at best most of the time. However, it will sometimes come on if I turn off the climate control then turn it back on after a couple of minutes. Unfortunately this is not consistant. Most of the time it just blows cool air. Almost like the system is not allowing enough air by the heater.
Any help appreciated.
thanks
martin

I will check it tonight, anything I should look for inparticular just not opening enough , a bad switch?

Yup search found me a nice website on how to do this. thanks again for the help. I will post on how it goes.
martin

you where right the mono valve had a tear in the rubber. I am ordering a new on tomorrow, hopefully that will fix the problem.

I have heat new mono valve worked