Quote:
Originally Posted by daddi
They are electric.
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The switches are electric. The doors and flaps are vacuum operated. If theres no vacuum, the system defaults to defrost.
The valve in the heater water line closes when vacuum is applied. I know from experience about this valve.
There is an elaborate electromagnetic vacuum valve set-up under the glove box. This controls your heater functions upon commands from the thermostat.
Mine had a crack in a vacuum line that caused the system to switch to defrost when I was climbing a steep hill, and switch back to normal after I let off the gas again.