Airmatic suspension not working properly

I would say the leak is in that corner and not the compressor as the other corners is staying up and they all use the same compressor. Most likely the issue is either a solenoid stuck or failed or an air leak. A stuck solenoid would act the same way as the air would be blocked and the computer would not see the height sensor going to the correct height and would keep running trying to move it. I would go check the control solenoid outputs first. Pop that line off that goes to that corner and see if air releases or not, you could use an air line and nozzle to put air into the system and see if it inflates or leaks. If it inflates the solenoid, is the issue. I believe you can have them rebuilt but with the current parts issues that could take a while. You might be able to make a line that at least lets you use a tire chuck to add air so you can drive it at least.

If the solenoid is stuck it could be that the pressure switch is shutting off the compressor. I would start with checking for leaks and work back from there, that way you don't replace the valves or compressor and then find that you need to replace the air springs as well.

Stuck solenoid. With it open and no load it worked, being it's sticking you could try an old trick, jack it up so you can get to the lines at all four corners and remove them. Now go to the accumulator (air tank) and remove the line on it. Now for the trick, take a cup of rubbing alcohol, add about two tablespoons of marvel mystery oil to it, shake it well and use a fluid injector/syringe/whatever to put about 1/4 of the mix into the line. Reconnect it, Now go to the air line manifold and pull the other end of the line off and shoot some of the mix into the control manifold so it will get between the solenoids and the compressor, you want it to be blown through them as they cycle. Leave the lines off at the bags and start it up, the compressor should start pushing the mix through the system and it will clean out and lightly lube the moving parts, once you see it spraying out the lines let it run until most of it is gone, reconnect everything and see if it acts better. I've used that on older Cadillacs and Lincolns with air ride because the solenoids get corroded from the moisture in the air and then start sticking. Usually this will work for years after being treated and is a lot cheaper than replacing the control head solenoid assembly.

Just don't do like one guy who read about it did, he decided that adding it after the compressor was more work than he liked so he added it to the intake port side of the compressor, didn't take into account that fluids don't compress very well. He had to replace the compressor after it locked up and broke the motor shaft off! It's the same type of thing truck drivers do to keep valves from getting stuck on big trucks.

Yep, the alcohol will flush dirt and moisture out and the light oil will lube the valves, letting it flow freely means it doesn't build up in the bags where it isn't needed. Sounds like you understand the system pretty well. That's a good thing.