Heater Control Valve Vacuum Question

[sawmkw]

I see that there is a vacuum line to some sort of canister switch on the firewall of my 96 Tahoe. There is manifold vacuum present to that switch but no vacuum out to the heater control valve. When is vacuum present to the heater control valve? With AC on or without? I'm trying to diagnose a no heat problem.

 

[sntrym95]

I had the same problem on my Yukon. When the AC is turned on, the heater valve stops the flow to the heater core. I simply removed the valve and ran the outlet from the intake manifold to the heater core. Problem fixed, and the AC works fine as well.

 

[next635]

I would like to read about it anymore. Prompt, what literature to study?

 

[next635]

I would like to read about it anymore. Prompt, what literature to study?
MyCVSHR