I just picked up a 97 Expedition EB in a trade deal, that I am fixing up for my wife to drive and to tow our small travel trailer with. It has the 4 wheel LLS system. I am trying to keep it working as oposed to converting it. One for keeping it level while towing, and 2, I really like that it lifts itself in low range, as I live in the snow, and sometimes the plow pushes a berm after I leave that my wife has to back over.
The previous owner put in new rear air bags. I replaced the bad union above the abs module. And I found an almost new arnott compressor in a navigator at the junk yard I grabbed. The system is working completely correctly, except that the compressor cycles very frequently. When I put it in drive, the compressor comes on, front and rear raise about and inch, the compressor shuts off. Then in about 30 seconds to a minute later, the compressor runs again. I have sprayed every thing for leaks and so far have not found one. I can get out with it in drive, engine off, and watch the suspension level sensors. After the initial air up, I cannot see any movement at all in the front or rear suspension, yet the compressor will come back on a run 15-30 seconds then stop a minute or so and start again. All with no detectable movement of the suspension. I have tried a couple used level sensors to see if they made a difference. They did not .If I put it in low range, it will raise another inch, and the compressor dosent seem to cycle much.
I would think that if there was a leak causing the compressor to cycle, I should be seeing some amount of movement at the level sensors, causing the compressor to come on.
Any ideas?

 

Let it pump up then unplug the compressor and go for a drive to see if the suspension lowers. The air might only leak out when the vehicle is moving up and down.

 

But then, why does the compressor keep kicking on when it's sitting in my driveway not moving? As long as it's in drive with the key on, even sitting stationary with me outside it measuring the suspension, the compressor keeps cycling on. Anyone know if high end snap on scanners will read suspension data? Or only ford software?

 

You didn't really make that overly clear since you said it happens when you put it in drive, which to me, would indicate that as long as it's sitting still in Park everything is fine.

 

So it seems after swapping the level sensors around and driving it around a bit, the compressor has calmed down and only runs occasionally while driving around, seems about normal now.