I have been trying to solve an issue with the climate control system in my 1994 E320 Wagon. I have replaced the dash controls with a module plucked from a yard car. The problem did not change.

Basically, the air conditioner seems to work but the defrost vents and sometimes the side vents blow hot air, while the center blows cold...

Any thoughts on where to look next?

 

Any takers out there? I could really use some help with summer approaching it's doing no good to have 3 ducts blowing hot air, and 2 blowing cold.

 

Hey bro just fixed this problem on my car.Theres a valve called the Mono valve that sits right in front of the battery, it also has a small circulator pump right next to it. These operate the cirulation of hot water to your heater core, but the diaphram in the vavle sometimes goes and it doesnt stop the circulation resulting in the problem your having. I bought a used one off a 95 E320 and seems to be working just fine because this is a verypricy part ($200+) you could also open it up and clean it some people that has worked for once the diaphram didnt fail like mines.Get back to me if u need more info........

 

spdeisel -

Simmzz is correct that the monovalve fails open and that is likely to cause what you are experiencing. But the mono valve is also open if no control voltage is applied to it, so before you replace it, you should check to make sure that 11 - 12 volts is present at the connector to the valve. If not, the problem lies elsewhere. The monovalve is the smaller of the two near the right strut tower (about the size of a D cell). Check for voltage with a meter (or you can use this $2.00 LED from Shadio Rack LED w/ resistor) by pulling the connector off when you are experiencing the problem you describe. If voltage is present, the valve is bad. If not further diagnosis is needed.

The best way to perform that diagnosis, if needed, is to let the system tell you what is wrong. To do that, build (or get a friend to build) the home-made code reader circuit shown here: schematic and then read the fault codes per this document: blink_codes. The system will tell you what you need to know.

Hope this helps,

- FD

 

I have a 2005 C240 with same problem is result to fix this the same?