F 250 4WD Super Duty V10-6.8L VIN Z CNG (2003)
Heater Control Valve: Description and Operation
The heater control valve is actuated by the air inlet door vacuum circuit (manual climate control) or the heater control valve vacuum control circuit
(EATC). When the heater control valve is closed (full vacuum), coolant flow through the heater core is shut off and A/C cooling efficiency is increased.
