Well I have been dealing with this climate control problem for a long time now without any luck. First off, I can't get the heat to turn off. I have already replaced the heater valve and made sure that the vacuum is good to it. The problem is at the vacuum switching center for the climate control system. The switch that supplies vacuum to the heater valve is not operating. How do I test the central control unit to make sure that it is putting out the proper signal. That is my first problem.

Problem two:
I rigged something up to manually override the heat so that I wouldn't die in the summer. But now my A/C isn't working completely properly. I had it recharged yesterday. The compressor will only come on when I put it in extra A/C mode. In normal mode, the compressor will not come on at all. I checked both the in the car temperature sensor and the A/C temperature sensor outside the car. They were both fine. It seems like it all comes down to the central control unit but I replaced my control unit with another used one. I think it would be a huge conincidence if both my old central climate control unit and my new one had the same problems. My A/C compressor also feels like it is slipping at higher RPMs. Does this mean the clutch is going out?
ANY HELP IS APPRECIATED!!!!!!
Thankyou very much anyone who contributes to solving my problem!

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George Carstens

high chance of vac leak in sys causing eratic blend air pod
, potentiameter fault. common sources are vacume elements,
or batt acid damage to red vac line to vac resevior.
good luck

I have checked all of the vacuum lines and elements. I only have one bad element and that is the one on top of the dash that can't be accessed without removing the dash....I blocked it off though so I would not be loosing vacuum. I know for a fact that my problems lies in the fact that my valves are not opening to let vacuum get to the heater valve.

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George Carstens

Constant heat is often the result of a failed Monovalve! I'm not sure of your model but the late 80's cars usually have the Monovalve located somewhere on or behind the engine compartment firewall probably on the passenger side. You can very easily and simply check the condition of the plunger by removing four screws, it is quick and easy to do.

Although the info is for a 126 Diesel car your car probably has the same system maybe in a slightly different place. Take a look!

http://mbdieseldiy.tripod.com/monovalve.htm

Good Luck!

Mono Valve = heater valve

I have already replaced this with a new one and checked the vacuum connections for leaks.

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George Carstens

blocking the vac line to the element on top of the heater
box cuts out one part of the resister chain for the push panel
it needs to compare the blend air door reostat volts to the
outside, inside and temp wheel settings. dollars to donuts
settting your blend air element and reostat right will
allow you to test the system as it was designed.

Make sure the belt is tight. The compressor has a built in RPM sensor and if the rpm of the compressor and the engine differs it will shut down the compressor.

You have replaced the heater (mono) valve, but have you checked the signal to it? I don't know, but I expect that it gets a signal from the pushbutton control unit as does the 124 cars. On the 124 cars a voltage to the valve SHUTS IT OFF. Use a voltmeter at the valve to see if it is getting voltage.

Surely someone here knows if this works in a normally open position or not.

Good luck,

I know that with vacuum, the valve is closed. This means that the valve on the controler is open. I don't know which terminals to probe in order to figure out if it is working properly. I went though the wire diagrams and there is supposed to be two wires that actuate the valve. I can't figure it out though.

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George Carstens