Heater Control Valve: Description and Operation

The heater bypass valve controls coolant flow through the heater core. A spring-loaded valve inside the housing allows coolant to bypass the heater core. It is normally closed at low coolant flow rates so all coolant passes through the heater core.

At increased engine speeds, this valve begins to open and controls maximum flow through the heater core to 5-6 gal/min by bypassing the excess. This amount is adequate for all heat requirements and prevents long term erosion/corrosion of the heater core due to excessive flow rates.