A Lincoln Town Car's air suspension uses a small, separate air compressor under the driver’s side left fenderwell, and air lines run to the air bags. On top of each air bag is a electrical valve that serves as a relief valve that allows air to be exhausted when activated. The valve senses the amount of air pressure within the air bag to keep both sides equal. These valves are operated via a leveling sensor that is attached to the body of the car and to the rear axle by a movable arm. When the rear of the car drops because of an increased load, the arm is pushed up, turning on the air compressor and filling the air bags to level the car. When the load is removed and the arm moves down, indicating that the back of the car has risen, the sensor opens the valve on the air bags and allows air to escape, lowering the car.
If the back of the car is low, indicating that the air suspension is not working, and the air suspension light is on, check the fuse. If the fuse is all right, make sure the air-suspension switch in the trunk is on. This switch is used when the car is in for service. Always turn off the switch before lifting the car, because the sensor will think the car is rising and keep the air bag valves open, ruining the rear air suspension.
Turn the ignition key with the engine off, and listen for the compressor to come on while pushing down on the rear bumper. If it does not come on, test the switch terminals for power with a circuit tester. If one terminal has power and the other does not, replace the switch.
If there is power, turn the switch to the "Off" position, raise the vehicle and place it on jack stands in the rear. Inspect the leveling switch on the axle, making sure it is not bent and is connected. Use an ohmmeter for this test. Pull the electrical connector off the switch. Loosen the arm of the switch from the axle. Test the switch with the ohmmeter by checking across both terminals while slowly moving the arm. There should be no continuity with the arm down. As the arm is raised, there should be continuity. If not, replace the switch. If there was continuity, connect the arm and the electrical connector.
Put a floor jack under the axle and raise the axle so it is just beginning to lift the car off the jack stand. Turn on the ignition. Turn the air suspension switch to the "On" position. Use the circuit tester to check for power at the leveling switch. If there is power, turn the air-suspension switch to “Off” and lower the car.
Access the air compressor in the front, under the hood, and check the electrical connector for power. If there is power, check for a good ground. If both are good, replace the compressor. If the compressor works and the car does not rise in the back, replace the air bags.