I have a central pneumatic 21/2HP 10 gallon 125 psi air compressor model 67708 that I picked up used. I checked it out for obvious damage, disconnects and leaks, all seemed fine. The oil has been changed as well.

The unit does not build pressure greater than 40 psi when it does run. Often it just shuts off with no regularity. I can hit reset and it continues to go intermittently.

My question is, may I jumper around the pressure switch as a check for a faulty pressure switch? If so, which side of the switch is the input side, so says Tom K?

Central Pneumatic 66708 air compressor

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You can if you have working pressure gauge. Sounds like you do. Just follow the wires from the plug and there you are. If the thing has capacitors, check them, Doug from s.d.ca.

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I found what I believe to be an image of the 67708 and uploaded it above for folks to see what type of compressor we’re talking about. If this isn’t similar to your own, please add a comment and upload a photo or two of your Central Pneumatic 67708 if you would.

Further to Doug’s comment, I certainly agree, you can bypass the switch with care.

The caution note is, you must make sure you are monitoring the pressure continuously as you power the compressor with the pressure switch taken out of the circuit. The pressure switch is the “first line of defense” in terms of preventing the overpressurization of the compressor tank.

The “2nd line of defense” is the pressure relief valve, typically set about 10-15 PSI higher than the normal cut out pressure setting of that pressure switch. If you remove the pressure switch from the circuit, the only thing that can prevent an over pressure is the PRV, and if that should fail, that could be a life-threatening situation.

So please, if you run the compressor with the pressure switch taken out of the circuit, watch the tank pressure gauge carefully and be prepared to shut down the compressor should the pressure mount too high.

Now, if you removed the cover of the pressure switch and see where the power cord enters, note where the white and black lines in the cord are attached. These are the Line / Supply terminals of the pressure switch.

On the other side of the switch you’ll see where the cord from the switch to the motor is attached to the pressure switch. That side of the pressure switch has the Load / Motor terminals.

Removing the power cord and motor cord lines from the pressure switch terminals and joining like colors will allow power to flow to the motor outside of and bypassing the pressure switch.

Do so with adequate care for live wires and to ensure that the compressor doesn’t over pressure.