Description & Operation

As altitude increases, air pressure decreases and air/fuel mixture becomes richer. High Altitude Compensation (HAC) system supplies additional air to primary low and high speed circuits on all models, and secondary high speed circuits on some models. This helps reduce emissions and improve driveability. Ignition timing is advanced for better driveability.

HAC system is designed to be functional at all altitudes. When altitude is above 3930 feet, HAC valve bellows expand and supply additional air. Components vary between the different models. See Fig 1- Fig 6 .

Fig 1: HAC System Components (Corolla FX W/Manual Transaxle)

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Fig 2: HAC System Components (Corolla FX W/Automatic Transaxle)

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Fig 3: HAC System Components (Tercel Wagon)

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Fig 4: HAC System Components (Tercel Sedan)

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Fig 5: HAC System Components (HAC & EBCV Corolla, Except FX)

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Fig 6: HAC System Components (Pickup)

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