For 1990-2009 cars

As the vehicle load decreases, the vehicle body raises, causing the automatic level control sensor arm to rotate downward. If the body raises enough so that the sensor arm rotates below the in-trim zone, the automatic level control sensor activates the internal timing circuit. If the vehicle maintains this condition for more than the minimum delay of 17-27 seconds, the automatic level control sensor completes the exhaust solenoid circuit ground. When the exhaust solenoid circuit energizes, compressed air exhausts from the shocks, through the airliners, air dryer, exhaust solenoid and automatic level control air compressor filter. The vehicle body then begins to lower.

As the vehicle body lowers, the automatic level control sensor arm begins to rotate upward. If enough load remains in the vehicle, the automatic level control sensor arm may reach the in-trim zone causing the automatic level control sensor to open the exhaust solenoid circuit. This de-energizes the exhaust solenoid and prevents further air from escaping the system. If very little or no load remains in the vehicle, the automatic level control sensor arm may not reach the in-trim zone. In this case, the automatic level control sensor de-energizes the exhaust solenoid after the electronic timer expires, approximately 5½ minutes. The system will then be at the minimum operating pressure of 55-97 kPa (8-14 psi).