too much heat

[kchemers]

89 300TE Car has automatic climate control, set the temp the blower goes on cabin heats up fan switches to low but won't maintain constant temp, cabin gets very warm. If I turn the temp down to the blue, fan kicks in air moves to the dash vents but they blow hot, only way to control temp of cabin is to turn the system off and wait for cabin to cool down, then turn system back on doesn't matter if I operate in economy or regular mode. System just started acting up was operating perfectly, cold a/c perfect heat, did I spring a freon leak????
Thanks kchemers

[platt-deutsch]

It may be the duovalve that controls the coolant to the heater cores.

[kchemers]

what is the duovalve and where is it located?

[platt-deutsch]

I dont know where it is on your vehicle. It will be installed somplace in the heater hoses before they enter the cabin. It is a solonoid valve that closes when it has voltage applied to it. If the electromagnet coil fails or if a piece of dirt gets under the plunger valve inside it will stay open and keep feeding hot water to the heater core.

[kchemers]

do you mean the monovalve??
anyway to test the part before I spend a $150.00 for a new one?
Thanks

[platt-deutsch]

Yes. on your car it May be a Monovalve. If you apply 12 volts to the coil on it there should be no heat in the cabin. If you dont have heat with 12 volts applied to the coil then the monovalve is fine and the problem is in the control system. Some have a duovalve that is the same as a monovalve but then there is not separate control for the left and right sides with the monovalve ..

[GoDiesel]

I have the same/similar problem, with Heat is ON all the time , in my 87 300 D Turbo.
Need help. here is description and some facts so far:

The ACC unit died so I bought one on ebay and it seemed to work OK for a while.
Then The Heat Start coming ON and stayed on.
I have removed / eliminated the Aux. pump ( which was corroded to death) and put a pipe in the hoses . Hot water definitely flows through, hence all the HEAT.

I have checked the Mono Valve, It works fine, w/ 12Volts applied to it, shuts down the heat. Thats how I have be turning the heat off, by hot wiring the Movo Valve.

I checked the voltage to the Mono Valve , here are the Voltage Values:
Everything Off, Car, main Elect off: 0 Volts ( obviously)
Engine on, but ACC OFF: 6.1 Volts ( I think it should be 12 V)
Engine on, and ACC ON: 6.2 Volts , with any Temp wheel setting (max cold to Max hot)
By the way, when moving the Temp wheel setting (max cold to Max hot), I do hear a click within the ACC , but he Voltage to MonoValve does not change from 6.1 V DC.

So, sounds like either another bad ACC or something else like the Cabin Temp Sensor or What else? Need help here...
How do I check Cabin temp sensor?
or whatever else?
My 1987 300 D Turbo body is 124.133
I think my ACC part number is 124.830.18.85 ( It was some how discarded , when I bought a "similar" but not exact part number from ebay)
It is hard to find the exact part number ACC.
Can someone tell me what other ACC models would be compatible w/ my car?

Thank you all.