zymurgist

I have a '77 with A/C. I am installing a new heater core. When I disassembled the heater/AC box, I found that the black plastic vacuum switch (a/k/a water shut-off valve, according to my GM documentation) was not attached at all! This switch has a spring on the end which keeps the heater box door partially open when there is no vacuum. Is this correct? I can't find anything in the GM service manual or the Assembly Instruction Manual about any possible adjustments. Any comments from anyone who has "been there, done that" would be appreciated. Thanks!

Doc Rebuild

Ken,

I would really like to help you and show you exactly where there is a colored diagram illustrating the color and routing connection for that spring loaded push-button switch – but I am not permitted to give you the location. If that switch is not connected, I don’t see how you hot water valve closes. There are solutions to this Climate Control question available and there is only one color illustration that I am aware of.

Geoffrey Coenen
NCRS #2473
NCM Lifetime #105
Vettehead #18-1
Retired #1 56, 63, 67, 68, 68, 69, 75, 99 and I want more !

zymurgist

Actually, I am using one of your hose kits (9222-108). The diagram is pretty self-explanatory, but I was wondering whether the spring on that valve is supposed to leave the heater door in a half-open position... or when I connect the cable to the lever on top of the heater box, does the cable exert enough pressure to override the spring (and thus allow the door to be fully open or closed)? Hope I'm making myself clear... I've never gotten this deep into the vacuum system before.

lou

When you put your temp setting from hot to cold, the cable will pull the door shut and depress the button on the switch. When the button is pressed, it sends a vaccuum signal to the heater water shut off valve out in the engine compartment, which keeps hot water from circulating through the heater core. lou

zymurgist

A-haa! So that switch sends a vacuum signal rather than receives a vacuum signal, and the spring is there on the switch to ensure that the switch always opens when the lever is moved toward the "hot" position. Thanks Lou! I'll be able to finish installing the vacuum hoses today. (Got headlight hoses to tackle next...)

mrvette

These sorts of over engineering examples are why I just gave up on the stock heater controlls, and got a junkyard selection of late model electrical/vacuum interface solenoid controlls....from late HVAC systems....
NOW using them wired MY way with my James Bond 007 control panel, I can have heat, a/c, temp, and flow where I want it, when I want it, and not some damn predetermined 'programming' done at the factory....somehow it makes life simpler....

GENE