Component Tests and General Diagnostics

TAC Heat On Position:

2. Start the engine.
3. With engine cold and running, and ambient temperature in the engine compartment below 55°F, the heat control door in the snorkel should be in the up (heat on) position.
4. Depress the throttle rapidly (1/2 to 3/4 position) and release. The air valve should briefly remain stationary and then move toward the heat OFF position and then back to the heat ON position.
5. Warm the engine to normal operating temperature and observe the air valve. The air valve should be fully open to ambient air above 55°F
6. Stop the engine.
7. If the air valve does not function as described in the previous test, inspect for a mechanical bind in the snorkel, disconnected or leaking vacuum hoses, and vacuum leaks at the vacuum motor, air temperature sensor, or intake manifold.
8. If the air valve manually operates freely and the hoses are not leaking or disconnected, connect a vacuum hose from an intake manifold source directly to the vacuum motor and start the engine.
9. If the air valve closes, the air temperature sensor is defective and must be replaced. If the air valve does not close, replace the vacuum motor.

AIR TEMPERATURE SENSOR
1. Disconnect the vacuum hoses from the air temperature sensor at the air cleaner.
2. Connect an hand operated vacuum pump to the vacuum source side of the sensor and a vacuum gauge to the vacuum motor side of the sensor.
3. Apply 14 in. Hg vacuum to the sensor.
4. When the sensor temperature is below 40°F vacuum should be maintained.
5. Warm the sensor to above 55°F. The vacuum should not be maintained by the sensor. Replace the sensor if defective