RAM 1500 Truck 2WD V8-5.9L VIN Z LDC (1999)
Vacuum Check Valve HVAC: Description and Operation
SYSTEM OPERATION
A vacuum check valve is installed in the accessory vacuum supply line near the vacuum tap on the right side of the engine intake manifold. The
vacuum check valve is 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 heater-A/C mode and vehicle speed control
settings. It prevents the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load (low engine
vacuum) operation.
A second vacuum check valve is installed in the accessory vacuum supply line at the tee fitting near the dash panel in the engine compartment.
This check valve also helps to maintain the system vacuum needed to retain the selected heater-A/C mode settings, but isolates the heater-A/C
vacuum circuit from the vehicle speed control vacuum circuit. It prevents the vehicle speed control servo from bleeding down the heater-A/C
system vacuum during extended heavy engine load operation.
The vacuum check valve cannot be repaired and, if faulty or damaged, it must be replaced.
