GM Genuine Parts HVAC Heater Water Flow Control Valves are designed, engineered, and tested to rigorous standards, and are backed by General Motors. These HVAC heater water flow control valves control the flow of engine coolant through the heater core. The heater water flow control valve is closed when maximum A/C cooling is selected. GM Genuine Parts are the true OE parts installed during the production of or validated by General Motors for GM vehicles. Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE).