Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
High Altitude Compensation System: Description
The High Altitude Compensation (HAC) system is used on California vehicles and high altitude Federal models. As altitude increases, air pressure decreases and the air/fuel mixture becomes richer. The HAC system supplies additional air to the primary main well.
The system consists of a High Altitude Compensator (HAC), passages for additional bleed air and additional jet air and a vacuum delay valve (Auto. Trans. vehicles).
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.