Weird air compressor problem

The only time I ever had problems with something like that, it turned out to be one of the valves inside one of the air bags on the trailer. When parked, I could see the air bag wasn't holding air.

 

I doubt the problem is with your compressor idling at 600 or 625, or even 1600. Yes the faster the engine turns, the faster the compressor runs, the faster it will build presure.

But the problem was with you loosing air while at a red light. Does this sudden loss of air only occur while your foot is on the brakes? Because you said when you bump the accelerator the problem instantly goes away, which makes me believe it's cuz your foot is on the acc, and not the brakes at this point.

 

So with the engine # 600 rpm you loose air, but # 625 or higher you build air? Yeah?

Lets say you're sitting, parked in a TS with brakes set. Now you idle up to 625 or more, and build air untill the governor kicks out at 120 (ish)

As soon as the gov kicks out you go back to 600. Then what happens?

 

Could be a lot of things. Does it only do it during really cold weather? If so it could be a froze-up air dryer.
Does it only do it when the brakes are released? If so it could be a bad brake chamber.
Since you said something about the brake pedal it could be a bad footvalve.
Whatever it is you need to find it. Good-luck I wish you well

 

Check the unloader valves on the compressor, might be getting carboned up

 

It could also be the radiator fan the clutches on them are air operated. I had that problem and it took 3 trips to the shop before they finally figured it out.