To control the temperature in the passenger compartment, the driver operates a lever, slide, or dial on the dashboard that is attached to a heater valve. This valve, usually located at the rear of the engine compartment, controls how much hot coolant passes through the heater core (located behind the dashboard).
If it is no longer possible to turn the vehicle's heat on or off, or if the valve leaks coolant, replacement of the heater valve may be necessary.
To replace the heater valve, the cooling system is drained, coolant hoses and the control cable are removed from the heater valve, and the valve is replaced. The components are then reassembled, and the cooling system is filled with coolant. In some vehicles, the heater control valve may be located behind the dashboard, which adds complexity to this repair.