Spectrum L4-91.5 1.5L (1989)
Altitude Switch: 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.
