Thanks for the post Mark,

I would say no, the problem most likely does not lie with the Regulator or Pressure Switch.

The problem lies with the Pump itself, most likely the Piston (Compression) Ring and/or Reed Valves are damaged; this will not allow the pump to compress at all or you will get very low compression.

The Pressure Switch simply shuts the unit off when it reaches the max PSI point for the unit, but the Pump is most likely not pressurizing as it should, so the switch never has a chance to shut the unit off.

The Regulator simply allows you to 'regulate' the air to the hose/tool, but if the pump is only pressurizing the tank to 20 PSI, you won't be able to regulate more than 20 PSI to the hose, so the Regulator is not your problem.

I would call Harbor Freight (Central Pneumatic) and ask their customer service dept if they have any pump parts available for this model; they may not be available (we don't offer them).

You could always take the pump head off of the pump/motor assembly and inspect the Piston Ring and Valves yourself, but the problem will be obtaining the new parts.

I hope this helps!

- MTR