Air Cleaner - Thermostatic: Operation
When engine is cold, air is selected from exhaust manifold shroud. During the "open" position, vacuum is applied to vacuum motor operating the duct valve. See Fig 1 . Duct valve closes off fresh air supply. This allows heated air to enter air cleaner.
As engine becomes warm, temperature sensor operates, preventing vacuum from being applied to vacuum motor. In this "closed" position, duct valve closes off supply of heated air, allowing external air to flow through pick-up tube into air cleaner. See Fig 1 .
Cold-weather modulator controls inlet air temperature. Cold-weather modulator retains vacuum to maintain duct valve position. This is done during vacuum decrease due to acceleration. Cold-weather modulator will only operate at certain temperatures.