Thermostatic Air Cleaner: Description and Operation

ACL:

The ACL system is mounted on the air cleaner and consists of a vacuum motor, hot air control valve (damper valve), thermo sensor vacuum valve, air bleed valve, hot air tube and a cover around the exhaust manifold. The system is used to control the temperature of the intake air, providing heated air from around the exhaust manifold to promote efficient fuel atomization during cold start and engine warm up.

ACL Operation:

When the engine is cold, the thermo sensor vacuum valve applies manifold vacuum to the vacuum motor, which positions the damper valve to block cool ambient air and allow exhaust manifold heated air to enter the air cleaner through the hot air tube. If the engine is operated at wide open throttle or high speeds, the resultant drop in manifold vacuum allows the vacuum motor to let cool air in through the snorkel.

When the engine reaches operating temperature, the thermo sensor valve closes the vacuum source. The vacuum motor spring then moves the diaphragm back to its resting position, causing the damper valve to close the hot air tube and open the air cleaner snorkel to let in cool air.

Some applications use a delay valve on the hose connecting the vacuum motor to the thermo sensor. When vacuum in this hose drops for any reason, the check valve will bleed off the vacuum to the vacuum motor slowly.

Extended idling, heavy loads and high speed operation cause an increase in engine compartment temperature. Under these conditions, fuel vaporizes in the carburetor float bowl and enters the intake manifold, creating a rich condition. This results in rough idle and increased CO emissions. The air bleed valve responds to the increase in engine compartment temperature by opening to allow fresh air into the intake manifold to lean out the air/fuel mixture.