Intake Air Temperature Control System

TAC Heat Off Position:

1. With the engine not running, the air valve should be fully open to incoming ambient air (heat OFF position).

TAC Heat On Position:

2. Start engine and observe position of air valve. It should be fully closed to outside air (heat ON position).
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. Loosely attach the ambient air duct to the air cleaner and warm the engine to normal operating temperature.
5. Remove the ambient air duct and observe the air valve. It should be either fully open to ambient air or at a mixture position that provides the correct inlet air temperature to the carburetor.
6. Stop the engine and connect the ambient air duct to the air cleaner.
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
- Vacuum leaks at the vacuum motor, thermal switch, reverse delay valve, check valve, intake manifold or vacuum hoses.
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, either the thermal switch, reverse delay valve, or check valve is defective and must be replaced. If the air valve does not close, replace the vacuum motor.

Thermal Switch:

THERMAL SWITCH
1. Disconnect the vacuum hoses from the thermal switch.
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 switch.
4. When the sensor temperature is below 95°F vacuum should be maintained.
5. Warm the sensor to above 95°F. The air vent valve should open and decrease the vacuum to zero. Replace the switch if defective. The temperatures listed are nominal switching values.

REVERSE DELAY VALVE
1. Remove the vacuum hose from the end of the valve that is not black in color and apply an external vacuum of approximately 2-4 in. Hg.
2. Using a stopwatch, note the time required for atmospheric pressure to pass through valve and eliminate the vacuum.
3. Replace the valve if the time required to eliminate the vacuum is less than 4.5 seconds or more than 13.2 seconds.
4. Install reverse delay valve with the black end toward the air valve vacuum motor.