GM Prizm/Nova 1985-1993 Repair Guide

Hot Air Intake (HAI) System

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OPERATION



See Figures 1 and 2

This system directs hot air to the carburetor in cold weather to improve driveability and to prevent carburetor icing. With the air temperature in the air cleaner below 72°F (22°C), the atmospheric port in the hot idle compensation valve is closed, sending the full manifold vacuum signal to the hot air intake (HAI) diaphragm. The HAI diaphragm moves, opening the air control valve which directs the heated air (from the exhaust manifold) into the air cleaner.

Once the air cleaner temperature exceeds 84°F (29°C), the HIC atmospheric port is open allowing atmospheric pressure to act on the hot air intake diaphragm. This keeps the air control valve closed, allowing the intake air to come directly down the air cleaner's snorkel from outside the car. This air is always cooler than the air from around the exhaust manifold.



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Fig. Fig. 1: Hot air intake system components

TESTING



  1. Remove the air cleaner cover and cool the HIC valve by blowing compressed air on it.
  2.  
  3. Check that the air control valve closes the cool air passages at idle.
  4.  
  5. Reinstall the air cleaner cover and warm up the engine.
  6.  
  7. Check that the air control valve opens the cool air passage at idle.
  8.  
  9. Visually check the hoses and connections for cracks, leaks or damage.
  10.  



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Fig. Fig. 2: Hot air intake system operation chart

 
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