Intake Air Temperature Control System

TAC Air Valve (Heat Off Position):

TAC Air Valve (Heat On Position):

AIR VALVE VACUUM MOTOR TEST

1. With the engine not operating, observe the position of the air valve through the ambient air inlet duct at the air cleaner. The air valve should be fully open to incoming ambient air (heat OFF position).
2. Start the engine and observe the position of the air valve. It should be fully closed to incoming ambient air (heat ON position) below 21°C (70°F).
3. 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.
4. Warm the engine to normal operating temperature. Observe the ambient air duct and air valve. The air valve should be fully open to ambient air above 21°C (70°F).
5. Turn the engine off.
6. 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.

TAC Vacuum Motor:

7. 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.
8. 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.

TAC Temperature Sensor:

AIR TEMPERATURE SENSOR TEST

1. Disconnect the vacuum hoses from the air temperature sensor.
2. Connect a 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 16 in. Hg vacuum to the sensor.
4. With the sensor at a temperature below 10°C (50°F) vacuum should hold.
5. Warm the sensor to above 21°C (70°)F. The vacuum should not hold. If vacuum is held, replace the sensor.