Thermostatic Air Cleaner: Operation
When the engine is cold, air is selected from the exhaust manifold shroud because the heat sensor in the air cleaner is cold. Vacuum is applied to the vacuum motor that operates the duct valve, and the duct valve is opened to allow heated air to enter the air cleaner. As the engine warms up, the sensor operates, preventing vacuum from being applied to the vacuum motor. The duct valve then opens and allows air from the outside to flow through the pickup tube into the air cleaner. A cold-weather modulator, on some models, controls operation of the duct valve under certain air temperature conditions for improved emission control.