Thermostatic Air Cleaner: Description and Operation

The Inlet Air Temperature Control System is designed to improve fuel atomization, by supplying warm air to the induction system instead of cold air. This reduces exhaust emissions during cold engine operation.

Air Cleaner Assembly:

Components within the Inlet Air Temperature Control System are: a Bimetallic Temperature Sensor, a Vacuum Delay Valve, a Cold Weather Modulator (CWM), a Vacuum Motor which controls the Air Duct Door, a Hot Air Tube and a Heat Stove Assembly.

HEAT SHROUD AND HOT AIR TUBE
A heat shroud is placed over the exhaust manifold with an approximate clearance of 1-2". As the exhaust manifold heats up, the air between the manifold and the shroud is warmed. The warm air travels up through the air tube to the air duct door.


COLD WEATHER MODULATOR (CWM)
The CWM is located within the vacuum line routing between the manifold vacuum source and the vacuum motor. Similar in shape and size to the bi-metal sensor, the CWM is mounted on or within the air cleaner assembly.

Operation Of The Cold Weather Modulator:

During cold weather operation, the bi-metal sensor is in its seated position against the check valve within the modulator. The bimetallic strip rests against the check valve's vacuum bleed vent opening.
When manifold vacuum drops suddenly, the check valve within the modulator becomes seated and vacuum to the vacuum motor is trapped. This ensures that the vacuum motor continues to hold the air duct door, allowing warm air entry.
Once the bimetallic strip reaches a calibrated temperature, it moves to its unseated position and opens the vacuum bleed vent of the check valve. This causes the vacuum motor to close the warm air inlet passage, opening the fresh air passage.


BI-METAL TEMPERATURE SENSOR
This sensor is mounted on the base or within the air cleaner assembly and is responsive to the temperature of incoming air. The bi-metal sensor routes vacuum to the vacuum motor until the incoming air reaches a pre-calibrated temperature. Color codes painted on the sensor help to identify temperature setting, bleed setting, and vacuum output.

Operation Of The Bi-Metal Sensor:

Manifold vacuum is applied to one of the nipples on the underside of the sensor. While incoming air is cold, the bi-metal sensor closes its vacuum bleed, directing full manifold vacuum to the vacuum motor. As the incoming air begins to warm, the bi-metal sensor begins to bleed manifold vacuum, thus reducing the amount of vacuum being applied to the vacuum motor. Once the sensor reaches its calibrated temperature setting, the bleed vent is fully open and no vacuum reaches the vacuum motor.
NOTE: Some bi-metal sensors contain a small check ball within the source vacuum hose nipple. The check ball is used to trap vacuum to the vacuum motor during a sudden decrease in manifold vacuum. This assures that the vacuum motor will hold the air duct door open.


VACUUM MOTOR AND AIR DUCT DOOR

Vacuum Motor And Duct Valve Operation:

When vacuum is applied to the vacuum chamber of the motor, the diaphragm within the vacuum chambers is drawn upward against spring pressure. This movement causes the attached hinged door to close the cold/fresh air inlet passage and open the heated air inlet passage.
As vacuum to the diaphragm chamber is decreased, the diaphragm is forced downward, and the air duct door either regulates between the inlet air passages or closes the heated air inlet passage.