W124 Cabin heat...its getting hot in here!

[Vladamir]

Ok, I know that this problem has probably been covered many a time, but I can't quite get to the bottom of the problem on my car, so I would be grateful if somebody could give me a step by step run down on likely problems.

First the car...its a 1986 W124 300E with NO Air-con.

Problem: No matter how much turning of the heater dials I do, the air ducts continue to blast out hot air......how do I get this fixed?

I've heard it could be the duovalves....I assume these are the two silver Bosch domes that sit infront of the brake servo. I've read that giving them a whack can unstick the solenoids...is this correct.

How else do I check to see if they are working and how easy are they to replace.

I've also read that the printed circuit board on the rear of the heater dials can fail....is this true and does it apply to non air-con cars? If so how do you get the wood trim off.

Any other suggestions.....please help before I disappear into a puddle of sweat

[mike690003]

I had a similar problem in my W124. It turns out that my heater core was not working correctly. It was stuck open and made my heater stay on. That lead to constant heat, and NO AC. When I replaced it my AC worked, and the constand heat stopped. The broken heater core made my AC and Heat stay on together, guess which one was stronger? The heat!


Get the heater core checked out, it might be the culprit.

[schumi]

there are a ton of reasons the ac may not work. first, check if the compressor is engaging and check the sight glass. those are easy to check with your eyes. do some searches here. then check if the high pressure switch is preventing compressor from engaging (again do some searches here, involves using a jumper wire to bypass the switch and takes 10 seconds).