Suspension Control ( Automatic - Electronic ): Description and Operation

CIRCUIT OPERATION

The electronic level control (ELC) keeps the rear of the vehicle at a constant height. If weight is added to the vehicle, the ELC height sensor turns on the ELC compressor. Air is pumped into the rear struts until the vehicle is level.

An actuator arm is connected between the rear axle control and the ELC height sensor, which is mounted on the body. It turns as the vehicle height changes. A solid state unit detects this motion and operates switches to control the air flow into and out of the rear struts.

Voltage is applied at all times to the ELC height sensor, ELC relay, ELC compressor assembly vent solenoid and inflator timer-relay. This allows the ELC system to lower the vehicle height with the ignition switch in OFF. Voltage is applied to terminal D of the ELC height sensor only with the ignition switch in RUN. The compressor, after an initial delay, will run for a few seconds to charge the system when the ignition switch is turned to RUN.

The ELC height sensor delays 17 to 27 seconds after a change in vehicle height before closing switch C in the ELC height sensor. This prevents system operation during normal ride motions. In addition, the ELC height sensor limits compressor run time or vent solenoid energized time to a maximum of 10 minutes.

This time limit is necessary to prevent continuous compressor operation in case of a severe system leak or continuous vent. Turning the ignition switch OFF and ON resets the 10 minutes maximum run time.

Raising the Vehicle
When a load is added to the vehicle, the vehicle body is moved downward and the actuator arm rotates upward. Switch B closes in the ELC height sensor. After a 17-27 second delay, switch C closes. The coil in the ELC relay is energized and the relay contacts close. Battery voltage is applied to the compressor motor. The compressor operates and pumps air into the adjustable rear struts. As the struts inflate, the vehicle body moves upward. When the actuator arm rotates back to its original position (plus or minus 1 inch), switch B opens, the relay is no longer energized and the compressor stops.

Lowering the Vehicle
When a load is removed from the vehicle, the vehicle body is moved upward and the actuator arm rotates downward. After a 17 to 27 second delay, switch C closes, the vent solenoid is energized and air is exhausted from the rear struts. As the vehicle body moves downward, the actuator arm is rotated back to its original position (plus or minus 1 inch), switch A opens and the vent is no longer energized.

Inflator
When air is needed to fill a tire, connecting the inflator hose and then turning the inflator switch to ON activates the inflator solenoid valve and ELC compressor. The ELC compressor pumps and air is diverted from the ELC system to the inflator system by the inflator solenoid valve.