HELP...compressor won't shut off

No terribly familiar with em, but don't they operate on a clutch like an A/C compressor? Could it be a seized up clutch?

 

Check the air govner should be on side of the compressor or it can be on the dryer itself depending on model is roughly 4" long round in shape with a few air lines running out of it and has a plastic cap that screws on one end

 

Compressor unloader, or governor stuck. It happens, better to be safe than sorry and just change both.

 

It could have only been a small piece of grit preventing the valve from closing. It sounds like the air governor. They only cost about $15 and are easy to install. If that doesn't stop the problem then you may want to check the air dryer. It will have a filter attached and should be somewhere around the frame rail. There are usually 2 lines and perhaps a wire connected to it. Next time it starts to leak, get out of the truck and check to see where it is actually coming from before replacing any parts. I think that I paid about $400 for the last air dryer that I had to replace.

 

You may also want to check the pressure release valve. It should be located on the side of your compressor. They just screw into the side of the compressor. You should be able to feel the air when it releases. I paid $34 for one about a year ago.