Maddog,
The question is, once you engage it does the compressor come back on while engaged? If not, there may be a leak but not in the air locker line. I diagnose line leaks by going to WalMart, buying a couple of bottles of kids bubbles, putting them in a garden sprayer and spraying the lines. If I see bubbles come out I fix the leak. Of course I don't use the ARB compressor, but it is the same concept. You may have a leak but from the sounds of it it isn't in the locker area.