No vacuum to heater core valve - 1991 GC

The only time vacuum is applied to that valve is when the HVAC controls are set to MAX air. IOWs, lack of vacuum is not the cause of your no heat condition.

Makes no sense, as Aarcuda said, you arent supposed to have vacuum there!! If you had to manually open the valve and got heat I would assume the valve is bad and not allowing it to open when the vacuum was off if you got heat after you manually opened it. The most common problem with lack of heat on that vehicle is a stuck open thermostat or a stuck blend air door. Google on how to check fault codes by cycling the key and looking at the check engine lite. If there is no code you may want to make sure that the cable is not sliding in the control assembly as you move it from hot to cold.

Glenn Beasley Chrysler Tech

Are you saying that this valve is always partially opened and that vacuum is applied to open it "all the way" whenever the max blower speed is selected?

Hello,

I had a similar setup on my 1987 Dodge 600SE years ago. The valve on that car was NORMALLY OPEN, and the vaccuum would be applied only when the controls are in RECIRC (i.e. MAX cool) to shut off the flow of hot water to the heater.

Thus, I suspect that the problem is with the valve itself in that it does not returen to it's normal position (probably rusted, etc).

Hope it helps,

Alex

Thanks Glenn and Aarcuda. Do either of you have any suggestions for checking the blend air door under the dash. What do you take apart to get at this? Thanks.

You have to remove the control head from the dash leaving cable connected and slide the control. If the outside cable housing is moving instead of the steel wire in the housing you can bet the door is seized up

Glenn