What is a thermostatic air cleaner?

Answer:

This system is designed to warm the air entering the carburetor when underhood temperatures are low, and to maintain a controlled air temperature into the carburetor or throttle body at all times. By allowing preheated air to enter, the amount of time the choke is on is reduced, resulting in better fuel economy and lower emissions. Engine warm-up time is also reduced.

The THERMAC system is composed of the air cleaner body, a filter, sensor unit, vacuum diaphragm, damper door, associated hoses and connections. Heat radiating from the exhaust manifold is trapped by a heat stove and is ducted to the air cleaner to supply heated air to the carburetor or throttle body. A movable door in the air cleaner case snorkel allows air to be drawn in from the heat stove (cold operation). The door position is controlled by the vacuum motor, which receives intake manifold vacuum as modulated by the temperature sensor.