See Figure 1
The rate at which fuel is drawn into the airstream in a carburetor varies with the temperature of the air that the fuel is being mixed with. The air/fuel ratio cannot be held constant for efficient fuel combustion with a wide range of air temperatures. Cold air being drawn into the engine causes a richer air/fuel mixture, and thus, more hydrocarbons in the exhaust gas. Hot air being drawn into the engine causes a leaner air/fuel mixture and more efficient combustion for less hydrocarbons in the exhaust gases.
The automatic temperature controlled air cleaner is designed so that the temperature of the ambient air being drawn into the engine is automatically controlled, to hold the temperature of the air and, consequently, the fuel/air ratio at a constant rate for efficient fuel combustion.
A temperature sensing vacuum switch controls vacuum applied to a vacuum motor operating a valve in the intake snorkel of the air cleaner. When the engine is cold or the air being drawn into the engine is cold, the vacuum motor opens the valve, allowing air heated by the exhaust manifold to be drawn into the engine. As the engine warms up, the temperature sensing unit shuts off the vacuum applied to the vacuum motor which allows the valve to close, shutting off the heated air and allowing cooler, outside (under hood) air to be drawn into the engine.
When the air around the temperature sensor of the unit mounted inside the air cleaner housing reaches 100°F (38°C), the sensor should block the flow of vacuum to the air control valve vacuum motor. When the temperature around the temperature sensor is below 100°F (38°C), the sensor should allow vacuum to pass onto the air valve vacuum motor thus blocking off the air cleaner snorkel to under hood (unheated) air.
When the temperature around the sensor is above 118°F (48°C), the air control valve should be completely open to under hood air.
If the air cleaner fails to operate correctly, check for loose or broken vacuum hoses. If the hoses are not the cause, replace the vacuum motor in the air cleaner.