Thermostatic Air Cleaner: Testing and Inspection

Fig. 24 Typical heated air intake system:

This system is used to maintain the temperature of the air entering the carburetor at a constant and predetermined temperature. In cold weather, this system directs a hot air supply to the carburetor to improve driveability and prevent carburetor icing.

When the engine is cold, the thermo valve is closed and the intake manifold acts on the diaphragm and draws it up. Raising the diaphragm causes the link to pull up the air control valve which closes the cold air passage and opens the hot air passage which is around the exhaust manifold, Fig. 24, acts on the diaphragm and the diaphragm is pushed down by spring tension. The air control valve is lowered to open the cold air passage and close the hot air passage.




Testing

1. Visually inspect vacuum hose air cleaner and vacuum operated door for damage and wear, and repair or replace as needed.
2. Remove air cleaner cover and cold air duct, if equipped, then cool thermovalve as needed to simulate cold engine operation.
3. Start engine and ensure that door closes off cold air duct to air cleaner.
4. Install air cleaner cover and warm engine. As engine warms, door should open cold air duct and block hot air duct to air cleaner.
5. If air door fails to operate, connect manifold vacuum directly to vacuum motor.
6. If door operates, replace thermo sensor. If door fails to operate with direct vacuum, replace vacuum diaphragm or repair door as needed.