Thermostatic Air Cleaner: Description and Operation

THERMAC Air Cleaner:

SYSTEM DESCRIPTION
The Thermostatic Air Cleaner (TAC) is designed to allow air to enter the air cleaner from outside the engine compartment, or from a heat stove built around the exhaust manifold. A Vacuum Diaphragm Motor, attached to the air cleaner snorkel, allows a damper door to control air flow entering the air cleaner housing. Inside the air cleaner housing is a temperature sensor that reacts to air temperature, and controls the amount of vacuum supplied to the Vacuum Diaphragm Motor.
When the air temperature is below 30°C (86°F), the sensor allows vacuum to flow to the vacuum motor. This causes the damper door to cut off outside air flow, and only heated air from the exhaust manifold will enter the air cleaner housing. When the air temperature is above 55°C (131°F), the damper door stops air flow from the exhaust manifold, and only outside air enters the air cleaner housing. Between these temperatures, the damper door combines air from both sources to maintain the proper air inlet temperature.

NOTE: Some applications use a delay valve in-line with the hose connecting the vacuum motor to the temperature sensor. If the vacuum drops abruptly, the delay valve allows for a gradual vacuum bleed off.