Thermostatic Air Cleaner: Description and Operation

PURPOSE
A heated intake air system is used for good driveability under varying climatic conditions. A uniform inlet air temperature improves fuel vaporization and reduces exhaust emissions by permitting leaner mixtures. The heated intake air system also improves cold engine performance and allows shorter cold enrichment periods. The Thermostatic Air Cleaner (THERMAC) is designed to keep air entering the engine between 100~-120~F.

CONSTRUCTION
The THERMAC includes a temperature sensor, vacuum motor, control damper and connecting vacuum hoses.

Thermostatic Air Cleaner Operation:

OPERATION
The temperature sensor controls the vacuum motor. The vacuum motor then operates the control damper, which regulates the flow of pre-heated and unheated air. The three operating modes are:
- Hot Air Delivery Mode: When the temperature is below 86~F, the sensor allows vacuum to the motor and the damper door will reduce outside air and allow heated air from the exhaust manifold to enter the air cleaner.
- Regulating Mode: Between 86~F and 131~F the damper door allows both heated air and outside air to enter the air cleaner.
- Outside Air Delivery Mode: When the temperature is above 131~F, the damper door drops down and outside air enters the air cleaner.

During periods of wide open throttle or when ambient temperatures are very high, there is not enough vacuum available to the vacuum motor to overcome diaphragm spring tension. The diaphragm then causes the control damper to move downward, closing the hot air duct and allowing only outside air to enter the air cleaner.

Thermostatic Air Cleaner With Delay Valve:

Thermostatic Air Cleaner Delay Valve
Some applications use a delay valve on the hose connecting the vacuum motor to the temperature sensor. When vacuum in this hose drops for any reason, the check valve will bleed off the vacuum to the vacuum motor slowly.