Thermostatic Air Cleaner Vacuum Switch: Description and Operation

Fig. 1 Bi-metal switch:

AIR TEMPERATURE CONTROL SENSOR

A vacuum operated duct valve with a thermostatic bi-metal switch, Fig. 1, is used. The valve in the duct assembly is in an open position when the engine is not operating. When the engine is operating at below 75° F, manifold vacuum is routed through the bi-metal switch to the vacuum motor to close the duct valve allowing only heated air to enter the air cleaner. When the engine reaches normal operating temperature, the bi-metal switch opens an air bleed which eliminates the vacuum and the duct valve opens, allowing only cold air to enter the air cleaner. During periods of acceleration the duct valve will open regardless of temperature due to the loss of manifold vacuum.

Fig. 2 Cold weather modulator:

COLD WEATHER MODULATOR

This modulator, Fig. 2, is used on some models to prevent the air cleaner door from opening when outside air is below a predetermined temperature. At higher ambient temperatures, the modulator is inoperative. During acceleration, with outside air below the preset temperature, the modulator will close off vacuum to the motor and hold the duct open. The modulator is located in-line between the air temperature control sensor and the vacuum duct motor.