RAM 3500 Truck 4WD L6-5.9L DSL Turbo VIN C (2002)
Vacuum Check Valve HVAC: Description and Operation
VACUUM CHECK VALVE
On models with a gasoline engine, 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.
On models with a diesel engine, a vacuum check valve is installed on the engine vacuum pump. 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 HVAC mode and vehicle speed control settings.
On gasoline engine models, it prevents the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load
(low engine vacuum) operation.
On diesel engine models, it prevents oil from contaminating the vacuum supply system by maintaining vacuum in the pump after the engine is shut-off.
On gasoline engine models, 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 HVAC mode settings, but isolates the
HVAC vacuum circuit from the vehicle speed control vacuum circuit. It prevents the vehicle speed control servo from bleeding down the HVAC system
vacuum during extended heavy engine load operation.
The vacuum check valve cannot be repaired and, if faulty or damaged, it must be replaced.