Thanks for the inquiry Terry. Most likely the on/off Pressure Switch is defective. You can take off the cast metal bottom portion of the switch, where it screws onto the electrical portion of the switch.

There is a rubber "gasket" or "diaphragm" in there and most likely there is a hole in the diaphragm that's causing air to leak out of it.

Unfortunately this isn't available separately but we do sell the Pressure Switch for this unit or a similar switch that will work for you.
Let me know what you will find and I'll be able to recommend a Pressure Switch that will work for you.
Thanks!
- MTR

To be safe you want to remove the Manifold from the Electrical portion of the Pressure Switch, where that Diaphragm is. I would do this to be safe but most likely you'll find it's deformed, has a tear or a hole in it which is allowing air to escape.

CP used a couple of different pressure switches on this same model, the easiest thing to do would be to point out which one of the attached switches looks like yours.
These are 125 psi switch (preset at that pressure). The most important spec is to confirm if you have a "Single Port" or "4-Port" switch, which is the number of threads on your manifold.

The first pic below is the Single Port, the second is the 4-port switch.

Also, are all threads the same size (usually 1/4") or different sizes?
- MTR