Vacuum Heat Control Valve: Operation

On cold starts, manifold vacuum is directed to VHC valve through the top two ports of the VHC PVS, closing the VHC valve against spring in vacuum motor. When engine coolant reaches a specified temperature. See VHC PVS IDENTIFICATION CHART . The VHC PVS shuts off vacuum supply and vents VHC valve vacuum to atmosphere when engine coolant temperature reaches PVS opening temperature value. This allows the spring in the vacuum motor to open the VHC butterfly valve.