Vacuum Check Valve

WARNING: This page is about a different car, the 2003 Jeep Grand Cherokee. However, it is still accessible from the selected car via links, so may be relevant.

Two vacuum check valves (non AZC only) are installed on the vacuum supply system. One is on the accessory vacuum supply line in the engine compartment, near the vacuum tap on the engine intake manifold. A second vacuum check valve is located on the bottom of the HVAC unit behind the passenger front floor duct on the black vacuum line. The vacuum check valves are designed to allow vacuum to flow in only one direction through the accessory vacuum supply circuits. The use of a vacuum check valve helps to maintain the system vacuum needed to retain the selected A/C Heater 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.