Thermostatic Air Cleaner: Description and Operation

Vacuum operated duct valve:

Bi-metal switch:

AIR TEMPERATURE CONTROL SENSOR

A vacuum operated duct valve with a thermostatic bi-metal switch is used on some installations, Figs. 1 and 2. The valve in the duct assembly is in an open position when the engine is not operating. When the engine is operating at below normal operating temperature, 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.

Cold weather modulator:

COLD WEATHER MODULATOR

This modulator, Fig. 3, located in the air cleaner housing of some Ford vehicles, prevents the air cleaner door from opening to non-heated outside air at ambient temperatures below 55~ F. At ambient temperatures above 55~ F, the modulator is inoperative. During acceleration at ambient temperatures below 55~ F, the modulator located in-line between the bi-metal sensor and vacuum duct motor, will close off vacuum to the motor and hold the duct open.