Altitude Compensator: Description and Operation

Altitude Sensing Switch:

The altitude switch consists of a bellows, called an aneroid, and a microswitch. The aneroid responds to atmospheric pressure. As altitude increases, the atmospheric pressure decreases. When the switch reaches a preset altitude - approximately 1220 meters (4000 ft.) - the aneroid will expand to close the switch, ground the solenoid, and signal the ECM.

High Altitude System:

The Altitude Switch closes the circuit between the battery and a solenoid valve and idle-up solenoid valve (high altitude). The Altitude Solenoid valve will open the passage between the air cleaner and the carburetor. Fresh air will pass through the three metering orifices and be supplied to the idle and off-idle system, as well as the primary and secondary main metering systems. The Altitude Mixture Bypass Solenoid valve will open the passage to the port downstream of the carburetor throttle valve, and additional air/fuel mixtures will be supplied to the engine for permitting stable idle rpm, even at high altitude.