Bypass Valves

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.

HVAC control contains a vacuum valve port that opens and closes hot water by-pass valve depending on switch position. Hot water by-pass valve is normally open and closes when vacuum is applied to it, only when MAX A/C mode is selected. Hot water by-pass valve controls engine coolant flow to heater core. When not in MAX A/C mode, vacuum is not present and by-pass valve opens allowing engine coolant to flow through heater core. The bypass valves included in the air temperature system are:

Coolant Bypass Valve
Hot Water Bypass Valve

The bypass valve is a normally open valve, which closes when vacuum is applied to the valve. When the MAX A/C mode is selected, vacuum from the HVAC control assembly is applied to the bypass valve. The vacuum must be strong enough to overcome the tension of the valves internal return spring in order to close the bypass valve. The return spring forces the valve to return to the open position, when any of the other HVAC modes are selected. In the closed position, the flow of coolant to the heater core is bypassed, allowing maximum cooling to the passenger compartment.