Thermostatic Air Cleaner: Description and Operation

As the rate of the fuel atomization varies with the temperature of ambient air, which in turn varies with atmospheric temperature, the air-fuel ratio cannot be held constant for efficient fuel combustion. This then allows harmful content in the exhaust gases to increase when the temperature of ambient air is inadequate for efficient fuel atomization. The automatic temperature-controlled air cleaner is designed so that the temperature of ambient air is automatically controlled to hold the fuel-air ratio constant for efficient fuel combustion.

The Air Cleaner (ACL) system consists principally of the thermosensor, vacuum motor, hot air control valve, and hot idle compensator. These components are mounted to the air cleaner body and snorkel.






(1) When the engine is cold started, the thermo sensor operates to deliver the maximum vacuum to the vacuum motor. This fully opens the hot air control (damper) valve. The ambient air passage through the snorkel is closed and the air passage from the hot air duct is opened.
If the engine speed is increased rapidly in this mode, the system vacuum level will fall, allowing the diaphragm spring to overcome the vacuum force and push the hot air control (damper) valve closed.






(2) Under normal engine operating conditions, the thermo sensor functions to close the passage from the intake manifold to the vacuum motor and open the passage from the air cleaner to the vacuum motor. As fresh air is fed to the vacuum motor, the diaphragm spring forces the air control valve to close the hot air duct while at the same time opening the ambient air passage through the snorkel.






(3) Extended idling, climbing a long steep slope, or running at high speeds for a long period of time will cause a marked increase in engine and engine compartment temperatures. This will cause excessive fuel vapor to enter the intake manifold, causing an over rich mixture resulting in rough idling and increased carbon monoxide emissions.
The hot idle compensator operates to prevent this by opening the passage from the air cleaner to the intake manifold. Fresh air is then fed to the intake manifold to lean out the over rich mixture.