Thermostatic Air Cleaner: Testing and Inspection

Fig. 33 Intake Air Control Diagram:

The operation of the various components that make up the Thermostatic Air Cleaner system during hot and cold engine conditions are illustrated in Fig. 33. The operation of each individual component during hot and cold running are as follows:

COLD ENGINE

Air Bleed Valve Closed, manifold vacuum builds.
Air Control Diaphragm Vacuum pulls up on air control door.
Air Control Door Rises, pre-heated air enters air cleaner (cold air blocked).
Check Valve Prevents vacuum loss at air control door during full throttle.
Fixed Orifice Prevents rapid pressure changes. Allows smooth operation of air control door.

HOT ENGINE

Air Bleed Valve Open, manifold vacuum bleeds off.
Air Control Diaphragm Internal spring pushes down on air control door.
Air Control Door Falls, outside air enters air cleaner, (heated air blocked.)
Check Valve Prevents vacuum loss at air control door during full throttle.
Fixed Orifice Prevents rapid pressure changes. Allows smooth operation of air control door.

Fig. 34 Intake Air Control Components:

COLD ENGINE SYSTEM TEST

1. Disconnect the air intake duct, Fig. 34.
2. With the engine cold, start the engine and let it run for about 5 seconds and switch it OFF. The air door should rise on start up and remain fully open for at least 3 seconds after the engine is stopped.
a. If the air door rises and holds, the cold operation is OK. Proceed with the hot engine test.
b. If the air door does not rise, first check to see if the door is binding.
c. If the air door is not binding but fails to rise, or is the door rises but fails to stay up for at least 3 seconds, proceed with the next step.
3. Disconnect and plug the hose leading to the air bleed valve inside the air cleaner.
4. Crank the engine for approximately 5 seconds and observe the operation of the air door.
a. If the door rises and stays up for at least 3 seconds, replace the air bleed valve and re-test.
b. If the air door does not rise or stay open, proceed to the next step.

Fig. 35 Intake Air Control Diaphragm And Air Control Door:

5. Disconnect the vacuum hose from the air control diaphragm, Fig. 35, and connect a vacuum pump to the diaphragm hose fitting and apply vacuum. The air door should rise and stay up.
a. If the air door does not rise and stay up. replace the air control diaphragm and re-test.
b. If the door rises and stays up, replace the check valve and re-test.

HOT ENGINE SYSTEM TEST

NOTE: As the outside air temperature drops, the bi-metal spring in the bleed valve closes, causing the air control door to rise and allow pre-heated air into the air cleaner. This allows the intake air temperature to be maintained at approximately 100°F.

1. With the engine running and the cooling fan ON, disconnect the air intake duct from the air cleaner snorkel and quickly check the position of the air control door. The door should be in the down position (shutting off the hot air).
a. If the air door has dropped down to cover the hot air duct, the system is OK. Shut the engine OFF and reconnect all hoses.
b. If the air door has not closed off the hot air duct, continue to the next step.

Fig. 36 Intake Air Control Components:

2. With the engine running, disconnect the vacuum hose from the air control diaphragm.
a. If the air door now covers the hot air duct, replace the air bleed valve, Fig. 36, and re-test.
b. If the air door does not close off the hot air duct, check that the air door is not binding. If it is not binding, replace the air control diaphragm and re-test.
3. Switch off the engine and reconnect the air intake duct.