General Motors THERMAC Air Cleaner: Operation

When temperature of air entering air cleaner is less than setting of temperature sensor, sensor closes to allow engine vacuum to operate vacuum motor which closes damper assembly to outside air. Air is then drawn from around exhaust manifold, through shroud and into cleaner as heated air. As air inside air cleaner warms, sensor valve begins to open, bleeding off vacuum to vacuum motor. This allows damper to begin to open to outside air. When temperature of air entering air cleaner reaches specified temperature, damper opens completely, closing off heated air inlet. Under full throttle conditions, vacuum cannot hold damper closed and allows only outside air to enter carburetor regardless of temperature.