ACDelco GM Original Equipment HVAC Heater Water Flow Control Valves control the flow of engine coolant through the heater core and are GM-recommended replacements for your vehicle’s original components. The heater water flow control valve is closed when maximum A/C cooling is selected. These original equipment HVAC heater water flow control valves have been manufactured to fit your GM vehicle, providing the same performance, durability, and service life you expect from General Motors.