Thermostatic Air Cleaner: Description and Operation

Intake Air Control System:

INTAKE AIR TEMPERATURE CONTROL
The intake air control system is designed to allow the carburetor to be calibrated leaner to aid in reducing HC and CO emissions during warm-up, improve cold engine driveability, and reduce carburetor icing. This system contains a vacuum motor within the air cleaner snorkel, a warm air duct hose, which connects the air cleaner to the exhaust manifold heat shield, and a thermo sensor mounted inside the air cleaner to detect the intake air flow temperature.
When the air inside the air cleaner is cold (less than 86°F) the bi-metal thermo sensor remains closed. Full manifold vacuum is applied to the vacuum motor. The vacuum motor pulls the air control valve door open and the warm air generated from around the exhaust manifold enters the carburetor. As the air temperature inside the air cleaner begins to warm-up, the bi-metal thermo sensor starts to modulate the vacuum being applied to the air control valve. The air control valve will drop slightly, due to the decrease in vacuum. This causes warm air to be mixed with the cool air of the engine compartment.
On a hot day or after the engine has been running for an extended length of time, the thermo sensor detects hot air within the air cleaner and opens to vent manifold vacuum to the atmosphere. No vacuum is applied to the vacuum motor, which causes the spring to close the air control door against the incoming hot air from the exhaust manifold.