you have a leak in one of your air bags, so neither side will air up until you change them or convert to springs or do some patch work, my suggestion is new air struts. one or both air struts are worn out.
jack the rear of the car up and let the air ride level itself once there down shut off air ride from the trunk
It is probably because of the rear air suspension... Lincolns have an "air" suspension which helps to give it a plush riding feel. There are bags near the wheels of each rear tire that are filled with air upon vehicle start up (or very shortly thereafter). These bags are filled with air has the vehicle is on, inflating if there is a drop in pressure. When the vehicle turns off, these bags are deflated thus lowering the rear end of the car.
Either one of your rear air bags have a leak or both have went bad.
check the air lines, there can be holes or cracks in the bags or the compressor is not working
Sounds like one of your rearend bags has a leak and won't pump up or the spider valve is stuck for the rear.
air
if you have more than 100k on it the rear bags have holes in them ,the fuse has blown cutting power to the pump that airs up the bags.
I own a 2001 Lincoln town car and i had a problem where the "air suspension" light was on in the instrument cluster and the rear end started to sag. turns out the air bags were leaking and the air compressor is designed to turn off in this situation to prevent the compressor from burning up. I ended up replacing the rear air bags with a coil spring kit which i found new for around $300 versus the more expensive new air bags. The ride was not noticably sacrificed but the "air suspension" light ramins on in the instrument cluster.
your rear suspension are air bags and they should be filling up automatically, if they are not then you have a leak, check for hissing sounds if they fill first and then go down, if they never air up then you have an air leak somewhere, the other side will not air up until the other side fills. you can get new air shocks at Suncore Industries online but be prepared to spend some change because their going to run about 200 with shipping. replacing them is going to be a b----- so have someone helping you, trust me.
your rear air bags need to be replaced. if you continue to operate the vehicle you will burn the pump up. It is also recommended you replace the dryer at the same time.
I don't think you can.
There is a switch that tells the system to release air from the bags. It is located behind the rear axle in front of the gas tank. A bar moves up and down and triggers the switch. It is about the size of a ball point pen. It may be disconnected or just not working.