I have a Harbor Freight (I know, I know) air compressor. It's the 21 gallon, 2 1/2 HP model.

The problem is that when the tank is empty it starts fine, and pressurizes the tank to where it should be. Once I start to use an air tool and the tank pressure drops below the trip point, the compressor will strain, not move, and then pop the breaker on the outlet strip. There is nothing else on that strip, it's just a way to extend the length of the power cord a short distance. The trip is slow, so the breaker in the strip is being strained, but not badly. If I empty the tank, it will immediately start up when I flip the power switch.

There is a valve in the top of the cylinder head, that seems to be there to allow the air trapped in the cylinder head to escape when the compressor first starts up. This allows the motor to get up to speed before trying to make it do any work. This seems to function correctly when the tank is empty. It lets the first 20 seconds of air out, then closes and the tank pressurizes. Can I assume it should do the same thing when the tank is just passed the refill pressure? I have not tested that it has, but I will.

One other thing, the freezer in the garage is on the same circuit. I have not tested a correlation between failing to start and the freezer running at the same time. How sensitive to voltage drops is a compressor this size? It's wired for 117AC by the way.

Oh, I thought it might be the compressor, so I returned the original one I had (same make and model) and the new one does it to. It must be something in my environment at home. I figure power, or temperature. It's been cold in the garage this season.

Oh, and I followed the instructions on oiling. I put the right kind of oil in it, ran it through break-in, plus another 30 minutes or so, and then changed the oil again. Nothing suspicious in the oil that I could see.

This is driving me nuts. Any thoughts?

1 Answer 1


The problem is you are over taxing the power strip. You need to power your compressor directly from the wall socket, or on an extension cord which can handle 15A or more (12 gauge or better below 50' length). Your compressor is rated at 14A, which usually means running Amps. When it first starts it will draw more amperage. When the tank is empty, it draws less Amps right off the bat because the pump is not working against pressure in the tank.

You really need to get it off the strip because you are killing your compressor.

  • I will do that tonight when I get home. The garage outlets are all GFI outlets. Do you think that will make a difference? I am a little embarrassed to say that I have no idea what effects ground fault interrupter outlets have on high current devices. -- The strip was one of the really beefy ones, all #12 wire in it. I figured it would be enough. I guess not. Thank you for the insight, this has been driving me nuts. I will of course play with it by rolling the compressor into the kitchen and trying it there plugged directly into an outlet. Should make the family very happy.. lol
    – cdunn
    Mar 8, 2016 at 21:48
  • The GFI will have no effect on anything. They only trip if there is a crossed circuit, it doesn't protect against surges. I would bet if you read through your compressor literature it will tell you something about not using a power strip. You really shouldn't use a power strip for any kind of electrical appliance, like a refrigerator or anything which will pull amperage anywhere near the max load. Mar 8, 2016 at 21:52
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    @cdunn I see you marked it answered, did his answer fix it? :-) Mar 8, 2016 at 23:09
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    I tested this tonight. Rolled the compressor into the kitchen and put it on its own outlet. Worked 100% as it should. Charged the tank, ran the grinder, and when the trip pressure was hit it started up exactly as it should. Thank you so much!
    – cdunn
    Mar 10, 2016 at 2:11
  • @cdunn - Awesome Bro! :o) Mar 10, 2016 at 2:39

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