Thermostatic Air Cleaner: Description and Operation

Fig. 23 Typical thermostatically controlled air cleaner system:

This system consists principally of the thermo sensor, vacuum motor, hot air control valve, and hot idle compensator. These components are mounted to the air cleaner body and snorkel, Fig. 23.

When the engine is OFF, no vacuum is present at the sensor unit or at the vacuum motor. The force of the vacuum motor spring closes off the ``heated air'' passage from the exhaust manifold heat stove, snorkel passage open.

When the engine is started cold, the thermo sensor is cool allowing maximum vacuum to the vacuum motor. Maximum vacuum at the vacuum motor completely opens the hot air control valve, closing off the ambient air passage through the snorkel and opening the air passage from the manifold heat stove. Should the engine be heavily accelerated while in this mode, the vacuum level in the system will drop to a low enough level so that the diaphragm spring will overcome the vacuum and open the snorkel passage.

As the engine heats up and the air past the thermo sensor reaches between 100°-111°F, the thermo sensor comes into operation and begins to bleed off the supply of vacuum from the intake manifold.

At approximately 111°F, the thermo sensor completely bleeds off all vacuum to the vacuum motor so that the diaphragm spring closes the hot air control valve to the heat stove passage and opens the ambient air passage through the snorkel.

Extended idling, climbing a slope or continuous high-speed driving is immediately followed by a considerable increase in engine and engine compartment temperature.

With this heat build-up, excessive fuel vapors enter the intake manifold causing an over rich mixture that results in rough idle and increased carbon monoxide emission. To prevent this, the air cleaner is equipped with a hot idle compensator. As the engine heats up and air past the hot idle compensator reaches a specified temperature, the compensator opens to feed ambient air into the intake manifold to lean out the temporarily rich mixture.