1994 E300D Heater stuck on maximum.

I have a problem with the heater on my 1994 E300D. Irrespective of the position of either of the temperature thumbwheels, the heater appears to be set to maximum temperature. Can anyone point me in the right
direction as to where the fault might lie?
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What about the airflow? Is it in Defrost vent regardless of setting? If so, then check the vacuum hose to the yellow checkvalves by the brake master cylinder. Make sure vacuum is good.
Do you have any other vacuum related problem?
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The airflow control appears to be working OK as does all of the fan speeds
"Tiger" wrote
> What about the airflow? Is it in Defrost vent regardless of > setting? If so, > then check the vacuum hose to the yellow checkvalves by the > brake master > cylinder. Make sure vacuum is good. > > Do you have any other vacuum related problem?
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I would take it to dealer... they can scan the climate control system to tell them what is wrong and then they can repair accordingly. I suspect the monovalve is bad but I don't see it on part list at online stores.
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I have an 82 300 TDT with version III of the auto climate control. I am guessing your '94 has a similar system. On vehicles with manual heat you move a lever that is connected via a cable to a valve that controls the flow of coolant theough the heater core.
On an automatic system an electrically controlled valve opens and closes when current is passed through an electrical coil/solenoid.
The valve can get contamination or sludge of some kind in it and then stick. Also there is a check valve that can get stuck open.
You should be flushing and renewing your antifreeze coolant on a annual basis, or crap will build up in the system and start ruining things like the auto control valve on your heater core.
Replacing the heater control valve is easy on my 300 TDT, it is in the open on the firewall above the engine. I just replaced mine and the part was less than $200.
Paul Fretheim alanc wrote:

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