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The 77 GM service manual shows this vacuum diagram for the vette, and in the middle of the diagram there is a water shut-off switch. Where on the car is this switch located? TIA, Mike
I should have been more clear. You are right about the valve (which is what I typed in the subject line). What I really want to know is the shut-off switch that sends the vacuum signal to the valve (as seen in the middle of the vacuum diagram)
The hot-cold lever goes to a cable that in the cold position, moves a temperature door that directs incoming air around the heater core. In the hot position, the cable pulls the door forcing the air through the heater core. According to the diagram, there is also some kind of vacuum switch that sends a vacuum signal to the heater control valve causing it to shut (it is in the open position when there is no vacuum).