Air Cleaner - Thermostatic: Operation
During an engine cold start the cool Inlet Air Temperature Compensator (ITC) valve delivers maximum vacuum to vacuum motor. This opens the hot air damper valve which allows air pressure from hot air duct to enter system.
Once engine is warmed, ITC valve closes the passage from intake manifold to vacuum motor and opens the passage from air cleaner to vacuum motor. This closes the hot air passage and allows ambient air to enter system.