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
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