Originally Posted by fuddyduddy121
Every single GM car that I have had will adjust the temperature of the air coming through the vents even though the system is off. Even the electronic climate controls will do that. However, the compressor will not operate.
Yes, there'* a vacuum feed to the temperature control (I'm oversimplifying here for the electronic controls) which is used to open and close the heater valve on the inlet hose to the heater core under the hood. That is, not only do you have temperature mixing doors in the dash which affect the temperature of the air being blown through the ducts, but also you have a valve in the heater hose that'* vacuum-operated to turn the coolant flow on and off.
So even when you have the blower off, the vacuum line can still open and close the heater hose valve, for what it'* worth. With the ducts closed and the blower off, you shouldn't get much if any hot air coming through anyway, but to be double sure about it, you can move the temperature setting to Cold as well.