High Altitude Compensation (HAC) System: Description
As altitude increases, the air/fuel mixture becomes richer due to loss of oxygen. This system insures proper air/fuel mixture by supplying additional air to the slow and/or high speed carburetor circuits when vehicle is equipped for high altitude operation (above 4000 feet). This minimizes hydrocarbon (HC) and carbon monoxide (CO) emissions and advances engine timing for improved performance. System typically consist of High Altitude Compensation (HAC) valve, check valve, and connecting vacuum hoses.