When a load is added to the vehicle, the vehicle body moves down causing the sensor actuating arm to rotate upward. (An arm movement of about 25 mm (1 in) amounts to a height change of about 12 mm (1/2 in) at the rear bumper.) The upward arm movement activates an internal timing circuit and, after an initial fixed delay of 17 to 27 seconds, the sensor provides a ground to complete the compressor relay circuit. The 12V (+) circuit to the compressor is then complete and the compressor runs, sending pressurized air to the struts through the air tubes.

As the struts inflate, the vehicle body moves upward rotating the actuating arm towards its original position. Once the body reaches its original height, +/- 25 mm (+/- 1 in), the sensor opens the compressor relay circuit, and the compressor is turned off.

In order to reduce current draw during air compressor starting, the height sensor performs an air compressor head relief sequence before air compressor operation. This sequence reduces the air pressure in the air compressor cylinder during start-up. The air compressor head relief sequence occurs as follows:

1. Exhaust solenoid is energized.
2. Air compressor is activated 1.3 seconds after the exhaust solenoid is energized.
3. Exhaust solenoid is de-energized 0.5 seconds after the air compressor is activated.

When a load is removed from the rear of the vehicle, the body rises, causing the sensor actuating arm to rotate downward. This again activates the internal timing circuit. After the initial fixed delay, the sensor provides a ground to complete the exhaust solenoid circuit, energizing the solenoid. Now, air starts exhausting out of the struts, back through the air dryer and exhaust solenoid valve, and into the atmosphere.

As the vehicle body lowers, the actuating arm rotates to its original position. When the vehicle body reaches its original height, +/- 25 mm (+/- 1 in), the sensor opens the exhaust solenoid circuit, which closes the exhaust solenoid and prevents air from escaping.

The sensor actuating arm position is checked when the ignition is turned on. If the sensor indicates that no height adjustment is needed, an internal timer circuit is activated. After about 35 to 55 seconds, the compressor is turned on for 3 to 5 seconds. This ensures that the struts are filled with the proper residual pressure. If weight is added to or removed from the vehicle during the time delay, the air replenishment cycle is overridden, and the vehicle rises or lowers after the normal delay.