Intake Air Temperature Control System

VACUUM CONTROLLED TAC SYSTEM CHECK
1. Disconnect ambient air duct and observe position of air diverter valve. It should be fully open to incoming ambient air (heat off position).
2. Start engine and observe position of air diverter valve. It should be fully closed to incoming ambient air (heat on position).
3. Quickly open throttle 1/2---3/4 open and release. Air diverter valve should momentarily remain stationary and then move toward heat off position and back to heat on position.
4. Loosely attach flexible ambient air duct and allow engine to reach normal operating temperature. Remove ambient air duct and observe air diverter valve. It should be either fully open to ambient air or an in between position that allows correct inlet air temperature. Stop engine and reconnect air duct.
5. If operation of diverter door is not as outlined, inspect for a mechanical bind in the snorkel, disconnected vacuum hoses or leaking vacuum motor, thermal switch, reverse delay valve and check valve.

TRAP DOOR TEST
1. With engine off, remove air cleaner cover and observe position of trap door. It should be closed.
2. Disconnect vacuum hose from intake manifold vacuum source and apply an external vacuum of 2---4 inches Hg. Trap door should open.
3. If door does not open, apply vacuum directly to vacuum motor on air cleaner intake duct. If door does not open, check for binding or distortion and adjust as necessary. Replace vacuum motor if door swings freely.
4. If door opens when vacuum is applied in step 3, inspect vacuum hose for obstructions, cracks and kinks. Correct as necessary and retest.
5. If vacuum hose is satisfactory, remove reverse delay valve, then join vacuum hoses and perform step 2. If door opens, replace reverse delay valve.

REVERSE DELAY VALVE TEST
This valve provides about 100 seconds of delay on 1983---88 models and about 375 seconds of delay on 1982 models before allowing the trap door to completely close.
1. Disconnect yellow hose from yellow end of valve and apply an external vacuum source of 2 to 4 inches Hg.
2. Note amount of time required for atmospheric pressure to pass through valve and eliminate vacuum.
3. Replace valve if amount of time noted in step 2 is less than 4.5 seconds or more than 13.2 seconds.

THERMAL SWITCH TEST
1. Disconnect hoses from thermal switch.
2. Connect vacuum pump and vacuum gauge to switch.
3. Apply 14 inches Hg to switch.
4. Valve should hold vacuum when its temperature is below 40° F and should release vacuum when switch temperature is above 55° F. Replace switch if defective.