No vacuum to heater core valve - 1991 GC

I have a problem with luke warm air coming from my heater. I just
recently found that I don't have vacuum at the heater core control
valve, so the valve is always closed (no water circulating in the
core). I manually opened the valve and now have heat. The vacuum line
is coming from the firewall. I assume I have a vacuum leak under the
dash somewhere. Does anyone have any suggestions where to start
troubleshooting and what to take apart under the dash? Thanks.

Ken

 

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