Vacuum Check Valve HVAC: Description and Operation

Vehicles equipped with A/C use vacuum to operate the recirculation door. A vacuum check valve is connected to the brake booster vacuum supply. The vacuum check valve is designed to allow vacuum to flow in only one direction through the accessory vacuum supply circuits and to stabilize the vacuum within the HVAC recirculation circuit whenever the vehicle is accelerating or engine vacuum varies due to operating conditions.

The use of a vacuum check valve helps to maintain the system vacuum needed to retain the selected heater-A/C mode settings. The check valve will prevent the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load (low engine vacuum) operation.

The vacuum check valve cannot be repaired and, if faulty or damaged, it must be replaced.