Question for you all-
Working on a small Ridgid air compressor. It has a compressor mounted to a small air tank, and has 2 additional tanks that snap on/off. Type for a trim nailer, etc.

The problem is that as soon as the compressor satisfies the pressure switch, the switch kicks off, and immediately there's a hissing noise. Pressure bleeds off from a port on the bottom side of the switch. It takes less than a second to dump the tank pressure below setpoint so the compressor tries to kick on again. Second or third time it does this it will trip the reset button.
The pressure switch has a stem sticking up that rotates. The Auto/Off dial attaches to it. While the cover is off you can press down on the stem and it opens the port where I'm leaking air from..
I can't figure out why the switch would need to bleed pressure. I have worked on this style pressure switch many times but this is a first for me.
it has a pop off valve on the outside of the switch and another for the auxiliary tanks. They seem to operate fine. Any input is appreciated, thanks.

 

Check valve in the tank is bad. The switch dumps the air from the compressor head so it starts easier on the next start up. The check valve at the tank has failed and and is back feeding through dumping the whole tank instead of just the head.

 

That would certainly explain it. It's still on the bench, will pull and inspect it. Thank you.

 

Just Chilling you nailed it. Good call, thanks!