Thermostatic Air Cleaner: Description and Operation

Fig. 35 Vacuum controlled thermostatic air cleaner. 1982---88:

This system provides heated air for the carburetor during engine warm-up. Heated intake air allows the carburetor air fuel mixture to be calibrated leaner to reduce hydrocarbon (HC) emissions. It also improves engine performance during warm-up and minimizes carburetor icing.
The system, Fig. 35, consists of a heat stove that partially encloses the exhaust manifold, a heated air tube, thermal vacuum switch, reverse delay valve(s), a check valve and a vacuum motor and air valve assembly.
The position of the air valve is controlled by manifold vacuum opposing spring tension. Manifold vacuum to the vacuum motor is controlled by the temperature sensitive thermal switch that is located in the air cleaner housing. This switch has an air vent valve that regulates vacuum applied to the vacuum motor and thereby controls the position of the air valve. The air supply is either all heated air, a mixture of heated and ambient air or all ambient air from outside of the vehicle. This regulation of air maintains the intake air to the carburetor at a near optimum temperature for the existing engine operating conditions. During high underhood air temperature or high ambient air temperature conditions, the air valve is maintained at the full heat off position to prevent excessively high temperature intake air from entering the carburetor.
To improve cold weather driveability on 1982---87 models, this system uses a reverse delay valve in the hose between the thermal switch and vacuum motor. Upon sudden acceleration (decrease in manifold vacuum) during cold weather operation, the delay valve momentarily maintains manifold vacuum at the vacuum motor and prevents an abrupt intake of cold ambient air, that may cause the engine to stall or hesitate. A one-way check valve, located between the thermal switch and the vacuum source, functions in conjunction with the reverse delay valve to prevent a sudden decrease in vacuum.