Compressor won't get past 120 PSI

So it never stops running.

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Bill answers...

Why can't the pressure in your tank get past 120 PSI and reach the cut-out pressure of your compressor?

First thing is to check your intake port on the pump to feel if air is blowing back out. If yes, valves.

The next most common is an internal gasket allowing air to blow by inside the pump, and not into the tank where it would increase the pressure.

Or, the motor hasn't enough ooomph (highly technical term) to overcome the backpressure in your tank when it reaches the 120 PSI level, or you've got enough "blow by" and slop in the pistons and seals that air, as it's being compressed, blows back past the piston seals instead of being forced into the tank against the 120 PSI that's already in there.

Or you've got a leak somewhere that appears at 120 PSI and bleeds off air at the same speed that it's being compressed.

Any leaks? Any air bleeding out of the pressure switch / unloader valve area, or out of a regulator?

If so, get 'em fixed. If not, get 'er into the shop.

Cheers,

Bill