I have a 99 DII with 160k mi.
The rear air suspension has been acting up lately. I searched the forums, but haven't found any threads describing the same problem.
First, I'll say that I can park the Disco for days with the suspension aired up, and it will not leak down. I have sprayed soap all over the air lines and compressor, all is good.
However, when I have some weight in the back, such as 2 passengers, camping gear and bikes, after a couple of hours driving the suspension will go down and the compressor will not come back on to air it up (yes, with the hood and all 5 doors shut)
Also, sometimes, when I park the truck, as soon as I get out and shut the door, the compressor will suddenly let all of the air out. I can hear it coming from the exhaust inside the rear fender. If I start the truck back up, and shut the door, it will air back up and keep all day.
Is there a solenoid or sensor that may be going bad?
The compressor is so expensive, if I have to replace it, I might as well go with the Terra Firma 2" MD kit and get rid of this headache all together.

 

yes, there are solenoid's in the same box as the compressor, you best bet is to email DM he knows quite a bit about the SLS and has been helping people save there systems rather than canalize it with coil springs