Vacuum heater valve 91 GC

After living with lukewarm heater performance for too long with my 91
GC, I decided to get to the bottom of the problem. I found no vacuum
to the heater core control valve. The vacuum line goes into the
firewall to the under side of the dash somewhere. What is the
suggested way to start troubleshooting and taking things apart under
the dash? TIA.

 

With a 15 year old vehicle you might consider bypass rather than
repair. For little money you could run a vacuum line from manifold
to a vacuum valve you just mount under the dash and manually
operate. Run a line from the valve to the heater core control valve.

Taking the dash apart is a very complex operation. The first step
is getting the factory service manual and studying the procedures.

Ted

 

You DON'T need a vacuum hose from the dash to the control valve!! The
purpose of the vacuum hose is to close the heater control valve when max air
is requested. Apply a vacuum source to the valve will cut off all incoming
hot coolant to the heater core.

Glenn

 

Thanks to Glenn, Ted and others for the advice. I understand how this
valve works now. I bought all new radiator and heater hoses and will
rip everything apart tomorrow. Hopefully after flushing the core a
little, the heat output will improve. Also bought a new t-stat from
Dodge. Two last questions; to flush the cooling system, can I just
open the petcock drain and put a garden hose in the top of the
radiator and let it circulate? Also, I hear about air in the system
causing problems and to "burp" the system. Just how do you do this?
Thanks all.

 

On older cars (and I'm going back *many* years), there was no valve on the
water input to the heater, just a direct (full flow) connection to the
heater core. The way the amount of heat was adjusted was by routing air
around the heater core. When the vacuum control valve on the heater water
pipe in one of my old cars died, I just hacksawed it off and connected the
hose directly to the remaining pipe. I was still able to adjust the amount
of heat I got, and no more funky vacuum control problems. (Another benefit
of a full flow connection is that flushing the cooling system flushed
*everything*.)