Thermostatic Air Cleaner: Description and Operation

Fig. 24 Thermostatically controlled air cleaner system:

This system, Fig. 24, includes the air cleaner, the air stove on the exhaust manifold, and the air intake hose connecting the air cleaner and air stove. The air cleaner is equipped with an air control valve which directs heated air to the carburetor intake when engine compartment temperatures are at 100°F.

In addition to reducing HC emissions, the system also serves to prevent carburetor icing and improve the warm-up characteristics of the engine. The temperature sensor detects the intake air temperature and opens or closes the vacuum passage between the intake manifold and vacuum motor.

The flame arrester prevents flames from entering the crankcase through the crankcase ventilation hoses in case back fire occurs. The air stove is mounted at the front end of the exhaust pipe. Fresh air is warmed up in this air stove and then introduced into the air cleaner through the air intake hose.

The air control valve is controlled by the inlet air temperature and the engine operating condition. The temperature sensor detects the inlet air temperature and controls the flow of vacuum to the vacuum motor.

When the underhood temperature is low and the intake manifold vacuum is high, the sensor valve remains closed and establishes vacuum passage from the intake manifold to the vacuum motor diaphragm. In this condition, the vacuum actuates the diaphragm which opens the air control valve to introduce hot air into the air cleaner through the air intake hose from the air stove.

When the underhood temperature is low but the intake manifold vacuum is too weak to actuate the diaphragm, the sensor valve remains closed and the air control valve closes the hot air passage, allowing only underhood air (cool air) into the air cleaner through its snorkel tube. When the underhood air temperature is high, the sensor valve opens fully to break the vacuum passage between the intake manifold and the vacuum motor diaphragm. In this condition, the diaphragm return spring presses the air control valve to close the hot air passage and the underhood air (cool air) is admitted into the air cleaner through its snorkel tube.

When the underhood air temperature is around 112°F, the sensor valve is partially opened and the opening of the air control valve varies with the vacuum from the intake manifold.

With the air control valve partially opened, cool air and hot air are drawn together and mixed, controlling the temperature of the air to be introduced to the air cleaner.