Heater Control Valve
A valve that regulates the flow of hot engine coolant into the heater core to control cabin heating temperature.
The heater control valve is an HVAC component that controls the flow of hot coolant from the engine block into the heater core inside the dashboard. By regulating this coolant flow, the valve controls how much heat is available to warm the passenger cabin.
Heater control valves can be controlled mechanically (via a cable connected to the dashboard temperature slider), vacuum-operated, or electronically controlled by the vehicle's climate control computer. When you select maximum heat, the valve opens fully, allowing hot coolant to heat the cabin blower air. When you select air conditioning, the valve closes completely, blocking hot coolant to keep the dashboard vents blowing cold.
Over time, the heater control valve can fail. If it sticks closed or becomes clogged, hot coolant cannot enter the heater core, resulting in no heat inside the cabin. If it sticks open, hot coolant flows constantly, which can cause the A/C system to blow warm or lukewarm air. The plastic body of the valve can also crack, causing engine coolant leaks.
Replacing a failing heater control valve is a common repair for cabin heating issues. After replacement, the cooling system must be topped off and bled to remove any trapped air pockets that could cause inconsistent heating or engine hot spots.