The ALC system controls the ride height of the rear of the vehicle. The system consists of the following components:

The level sensor senses the height of the rear of the vehicle. The exhaust valve energizes if the vehicle is higher than desired. The compressor relay energizes in order to activate the compressor assembly if the vehicle is lower than desired.

Voltage is applied at all times to the rear suspension leveling air compressor and the ALC sensor. This allows the ALC system to vent after the load is removed from the vehicle, even if the ignition is in the OFF position. Approximately 30 seconds after the ignition is turned to the ON position, the compressor will run for 4 seconds to ensure that the shock absorbers will be filled with adequate residual pressure.

The ALC sensor must detect an out of trim state for 20 seconds before activating the intake or exhaust output. This action prevents operation during normal riding motions. In addition, the sensor limits the compressor run time or the exhaust solenoid valve energized time to a maximum of 255 seconds. This time limit is necessary to prevent continuous compressor operation in case of a severe system leak or continuous vent. Cycling the ignition resets the 255 second run timer.

The ALC system for the cargo vans will work in the same manner but will not have the inflator option. There will be no accessory inflator switch LED for DTC diagnostics. The diagnostics will be symptom base

The compressor is a positive displacement rocking piston air pump powered by a 12-volt direct current permanent magnet motor. The compressor head casting contains the piston intake valves and contains the piston exhaust valves. The compressor is mounted to the underbody by a bracket.

The ALC sensor is an electronic device. The following is controlled by the ALC sensor:

The sensor circuitry provides a 20 second delay before either circuit can be completed to prevent falsely actuating the compressor or to prevent falsely actuating the solenoid valve circuits during normal ride motions.

The sensor also limits the compressor run time or the solenoid valve energized time to a maximum of 255 seconds. This time limit function is necessary to prevent continuous compressor operation in the case of a severe system leak or in the case of a continuous exhaust valve operation. Turning the ignition off and on resets the electronic timer to renew the 255 second maximum run time. The sensor is located in the rear of the vehicle mounted to the underbody. The actuator arm of the sensor attaches to the rear suspension by a link.

The ALC system will be capable of performing diagnostics on all components of the system. This self diagnostic feature will aid in the repair of the system. The diagnostic codes will be used to provide more detailed information regarding the system fault found during the self test. The self test will be entered by pressing the accessory inflator switch continuously for 3 seconds. The self test will begin by raising the rear of the vehicle. Then hold the rear of the vehicle up for a calibrated amount of time to check for leaks, then lower the rear of the vehicle to trim height. The self-test will take about 200 seconds to complete. The flashing pulses on the accessory inflator switch LED shall represent the number of the diagnostic code.

When the sensor has been replaced a "System Untested" code will be represented by a continuous flashing pulse with a repetition rate of 0.25 seconds. The self-test will have to be performed and a code 12 system OK will have to be displayed with the accessory inflator switch LED before the system can function normally.

The shock absorber is essentially a conventional shock absorber enclosed in an air chamber. The shock absorbers are constructed with a rubber-like sleeve attached to the dust tube and attached to the shock reservoir. This makes a flexible chamber which extends the shock when the air pressure in the chamber is increased. The weight of the vehicle collapses the shock absorber when the air pressure is reduced. To maintain proper operation and to maintain reliability of the shock absorber a minimum residual air pressure of 55 kPa (8 psi) is maintained at all times by the air dryer.

The snap-on connectors attach the tubing to the rear shock absorbers. The connector housings contain retainer clips. When a tubing is attached to a shock fitting, the retainer clip snaps into a groove in the shock fitting, locking the tubing in position. All tubing fittings are sealed with 2 O-rings.

The air enters the ALC system through the filter mounted to the air compressor bracket. The filter housing contains a foam filter which prevents contaminants from entering the ALC system.

The vehicle body is forced downward when a load is added to the vehicle. This load causes the sensor actuating arm to rotate upward. The upward movement of the sensor actuating arm activates the internal timing circuit. The sensor completes the compressor circuit to ground after an initial delay of 20 seconds. With the compressor circuit complete, the compressor runs, taking in air through the air compressor filter and sending the air though the tubing to the shock absorbers. As the shock absorbers inflate, the rear of the vehicle moves upward, rotating the sensor actuating arm back toward its original position prior to the load addition. The sensor opens the compressor circuit and shuts off the compressor once the body reaches its original height +/- 4 mm (+/- 0.16 in).

The body is forced upward when an excess load is removed from the rear of the vehicle. This causes the sensor actuating arm to rotate downward. The downward rotation of the actuating arm activates the internal timing circuit. The sensor completes the solenoid valve circuit to ground after an initial delay of 20 seconds. With the solenoid valve energized, the air begins to exhaust out of the shock absorbers back through the air dryer, the solenoid valve, the air compressor filter and into the atmosphere. The sensor actuating arm rotates upward toward its original position as the rear of the vehicle lowers. When the vehicle body reaches its original height +/- 4 mm (+/- 0.16 in), the sensor opens the solenoid circuit, de-energizing the solenoid valve, which prevents any further air from escaping.

The air replenishment cycle serves to ensure that the shock absorbers are filled with at least minimum residual pressure. The sensor commands an air replenishment cycle each time the ignition switch is turned on. Sensor position is checked when the ignition switch is turned on. If the sensor indicates that it is not necessary to raise or lower the vehicle, an internal timer circuit is activated. After a 30 second delay, the compressor is turned on for approximately 4 seconds. This ensures that the shock absorbers are filled with adequate residual pressure.

If the weight is added to, or removed from, the vehicle during the initial 30 second delay, the air replenishment cycle will be overridden and the vehicle will raise or lower after the normal delay.

A 1.5 second actuation of the exhaust solenoid valve occurs each time the compressor is to start to ensure the low compressor motor starting current. The 1.5 second actuation of the exhaust solenoid valve reduces the air pressure in the compressor head cavity.

Cargo vans will not have the inflator option.

The inflator solenoid has battery voltage to it at all times and is controlled buy the height sensor with providing a ground to the solenoid. The solenoid valve is mounted to the compressor bracket under the vehicle

The inflator switch is in the rear cargo area on the drivers side on the vehicle. Cargo vans will not have a inflator switch so all diagnostics will be symptom based and not DTC.

When the switch is depressed, the compressor is activated along with the inflator solenoid and air pressure is directed to the schrader valve that is located next to the Inflator switch. The LED on the switch is also on during the inflator function. Depress the switch again and the compressor and the LED are deactivated. The switch and LED are also used for diagnostics. Depress and hold the switch for 3 seconds and the system enters self test. After roughly 200 seconds the LED will blink out the diagnostic codes.