Vacuum Sensor / Switch HVAC: Description and Operation

Some vehicles are equipped with a heater control valve vacuum switch to control operation of the heater control valve. Presence of the heater control valve vacuum switch can be verified by visually inspecting the RH side of the heater core and evaporator core housing with the glove compartment lowered. The heater control valve vacuum switch:
- is mounted on the RH side of the heater core and evaporator core housing just below the defrost door vacuum control motor.
- is actuated by an arm attached to the temperature blend door RH pivot shaft.
- applies vacuum to the heater control valve when the temperature blend door is in the full COOL position.

The heater control valve is actuated by the recirculation air duct door vacuum circuit on vehicles not equipped with a heater control valve vacuum switch.