The rear air ride suspension on my 98 lincoln navigator left side has collapsed. The compressor does not kick in. What seems to be the problem?

Somewhere, ahead of the compressor, are relays and a fuse or two. Your Lincoln dealer should be able to tell you where to look, if you do not wish to take it to them.
I think under the hood is the first place to look, as that circuit is requiring a lot of current.
You have a black plastic cover over a black plastic box with fuses and circuit breakers in it under the hood, and you might find the air ride system named in that box with a corresponding fuse.
God bless your efforts.

Ford Air Ride Rear Suspension Down Diagnosis & Fix ...

? 9:57
https://www.youtube.com/watch?v=wfh7n17hvN8
Feb 24, 2014 - Uploaded by FordTechMakuloco
Ford Air Ride Rear Suspension Down Diagnosis & Fix ... why theair ride compressor is not turning on and pumping up the air ridesuspension on your truck. ... Ford Expedition & Lincoln Navigator Air Ride C1725 Common Faults ... 2000 Ford Expedition - Replacing the rear shocks with load leveling shocks ...

2003 Lincoln Navigator air suspension fix(3) - YouTube

? 3:41
https://www.youtube.com/watch?v=MhWlcYycny4

Fix your car right away by clicking the link I attached
Lincoln Navigator 1997 2002 WorkSHOP Service repair manual Download

My suggestion to you and all the other folks leaving questions on this board about collapsed air suspension systems in luxury cars is to fix that one by replacing it with a real spring and shock system which you can buy at www.strutmasters.com if it is economically feasible, then sell it and avoid air suspensions systems like the plague. There are legions of old 70s Citroens still sitting idle 30 years later on collapsed air suspensions systems in garages and barns all over the country which cars the buyers can't let go because they cost so damn much. Get a coleman air mattress and use it every day, see how long it really lasts.

Your problem is due to your car's air ride suspension being temporarily off line. This is likely because your air-ride suspension relay is blown. Simply replace the relay module located in a large black box under your hood. Take lid off of black box and find the air suspension module and replace. It will look like a square silver match box plugged into a circuit board. Unplugg it and replace it with a new one.

the most common problem in this truckr and the Ford expidition is that the rear suspension air springs are leaking, they last about 75,000 miles, less on really rough roads.

there is an air ride suspension in that vehicle.that is what sets the height.in the rear cargo area on the left side there is a cover.open it.there is an air ride switch.make sure it is on.there is a compressor as well check the fuse is ok.

email me @ [email protected]

is it doing this while driving or while parked?

Leveling sensors froze up ? Have you been through snow & slush?
Can the vehicle be stored in heated garage for a night?