All sorts of vehicles have air line antifreeze systems including modern ones, the point is that the air line antifreeze is introduced into the wet tank or some other location which is after the air dryer. The air line antifreeze is harmful to the desiccant in the air dryer, so it should not be introduced before the air dryer.
There are probably older installs before air dryers were common where the antifreeze was introduced right after the compressor, in which case they should probably be disabled or moved if an air dryer is retrofitted.
This sounds to me like the intake, discharge or unloader valves sticking. The air compressor continually compresses air, the unloader valve diverts it to atmosphere when told to by the governor. My manual says the unloader needs to be lubricated with a special lube, dimethyl polysiloxane, http://en.wikipedia.org/wiki/Polydimethylsiloxane
It will apparently lube your unloader, keep your hair shiny, and make your Chicken McNuggets tasty and crispy. I kid you not, the things you learn on a Friday morning on the Bus Forum...
Anyway, I think you need to service your compressor.