# Air compressor



## Jasonrkba (Oct 4, 2016)

I picked up a lightly used 26 gallon air compressor. I ran a long heavy gauge extension cord to power it up and it ran fine, cut off at about 125 lb but when it needed to crank back up it popped the breaker. I turned it off then flipped the breaker back. Now I turn it on and it starts for a second then humms. Shut it off then bleed it down to about 25lbs, turn it on and it runs fine. Any suggestions?

Thanks. Jason.


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## ANewSawyer (Oct 4, 2016)

Hmmm, I have read what causes that but don't remember what it is! It is on google somewhere.

Try this page: http://fix-my-compressor.com/air-compressor-just-hums/

http://fix-my-compressor.com/air-compressor-just-hums/


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## Jasonrkba (Oct 4, 2016)

Sears direct says change the check valve, that it is stuck open. 

Thanks. Jason.


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## Marshy (Oct 4, 2016)

Is the motor 110 or 220 volts? I'd suggest a larger gauge cord and proper breaker size.


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## mijdirtyjeep (Oct 4, 2016)

Mine was doing the same thing when I rebuilt it a few years back. What happened on mine is the little arm that contacts the unloaded valve was not making contact. This kept the air pressure in the line from the piston, and the motor could not overcome the pressure to get spinning up. It is pretty easy to see if it is working or not, and if you have your ear down by it when the pump cycles off, you will hear the air bleed out.


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## Jasonrkba (Oct 5, 2016)

It is 110. I ran a cord Because it's in the basement and we have the old two prong wiring down there. I just didn't feel comfortable cheating it. I do plan on rewiring it (the basement) in the future and the box has already been updated. 

Do you think it would pull more amps at startup if the tank is full as apposed to empty?


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## Ted Jenkins (Oct 5, 2016)

Your starter is worn out. Unless you do not have a typical compressor motor. If your motor has a metal cover with a 2 inch bulge then that is your problem. To replace them can be very tricky because the motor is not likely to be like new condition. I have replaced many starters to find out that the motor did not like them. So you may have to experiment a bit to get it just right. When you take the starter out not the run unit but the starter unit it will have a range of resistance so replace with the same range and hope all is well. If it burns up then go to a slightly more resistance unit or slightly less. I every once and awhile I see starter unit on sale so I buy several to have on hand. 
Thanks


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## Jasonrkba (Oct 5, 2016)

Is that the capacitor?


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## Ted Jenkins (Oct 5, 2016)

Yes sir. Thanks


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## Jasonrkba (Oct 5, 2016)

Makes sense. Do you think the long extension cord could be underpowering it? A quick search looks like the caps are around $40. Just hate to guess and it not work.


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## Jasonrkba (Oct 5, 2016)

Also is this what we are calling unloader valve?


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## mijdirtyjeep (Oct 5, 2016)

The black hose is going to feed the beeder (unloader valve). Trace that hose back to its source. The brass part is the check valve. It keeps air in the tank and allows the unloaded valve to bleed off air in the line without draining the tank


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## mijdirtyjeep (Oct 5, 2016)

This is the location of my unloader valve.


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## Ted Jenkins (Oct 5, 2016)

On my compressor the motor started to act up so my thought was to check the unloader so It got completely disconnected and it made no difference. So I added a hard start capacitor and still had problems. I ran into some one that understood motors better and recommended a higher torque motor which ran so well that I forgot about the unloader and all the other issues. The start units still have to be changed now and then, but not a big deal. I bought an assortment of caps more than 20 of them for $50 including shipping from the Surplus Center awhile back and still have about 15. Like every thing else if you shop around you can find deals, but would never pay more than $5 for a cap since they might work or not. Thanks


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## Jasonrkba (Oct 6, 2016)

I'm guessing one like this. I read that you should short the old one out by crossing the terminals with a screwdriver before removing. How does that discharge it if it still has power stored in it?


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## mijdirtyjeep (Oct 6, 2016)

Have you at least ruled out the unloader valve? All it is, is a tire schader valve. By simply pushing it up with a screw driver or just removing it for a trial you can at least rule that out.

the reason I believe it to be the unloader or check valve as you stated that


Jasonrkba said:


> Shut it off then bleed it down to about 25lbs, turn it on and it runs fine.


. So it should not be a capacitor problem, or an extension cord problem. Now a hard start capacitor probably can over come a defective unloader valve, so it will cure (mask) the problem as well.


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## Jasonrkba (Oct 6, 2016)

I haven't but I will.
I didn't know much about how compressors worked a week ago but that's sure changing.

Thanks for the help everyone.


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## Jasonrkba (Oct 6, 2016)

Seems it's integrated into the on off switch.


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## mijdirtyjeep (Oct 6, 2016)

need a pic from the top side


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## Jasonrkba (Oct 6, 2016)




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## Jasonrkba (Oct 6, 2016)




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## mijdirtyjeep (Oct 6, 2016)

LOL, I meant with the cover off


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## Jasonrkba (Oct 6, 2016)

Ok.lol
I'll have to get back. I'll have to remove the safty blow out to remove the plastic cover. Gotta go to work now.

Thanks. Jason.


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## mijdirtyjeep (Oct 6, 2016)

Actually I just got online and looked it up by the pic you posted. The black hose going into the bottom of the pressure switch is a quick disconnect. To test the unloader valve, just disconnect the hose after the pump has cycled off. Then run some air out of the tank to see if the compressor re-starts back up. If it does, you know the unloader is the problem. If air continues to leak out of that hose (pump not running) you know the check valve is bad. If neither of those work, either your extension cord is the problem, or your motor has a fault. That is easy to test as well. Just put the old cord back onto it and see if it works. You may have to drag it to a location that has a 3-prong outlet, or just cut the 3rd prong off and use it. These things are used in a garage anyways, so its not like it should get wet and electrocute you from not being grounded. Heck mine has been missing that 3rd prong for over 6yrs as I cut it off a long time ago..


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## Jasonrkba (Oct 6, 2016)

Good stuff!
Just found this video and I believe it is my part he's using.


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## BroncoRN (Oct 19, 2016)

How long and what gauge extension cord are you using? I would be using a 10 gauge cord and 100 ft at the max to minimize voltage drop.


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## Jasonrkba (Oct 19, 2016)

Not sure about the gauge. It's pretty thick, not a cheap orange one. It is a long one though.


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## Jasonrkba (Oct 25, 2016)

Removed the check valve.lol


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## ANewSawyer (Oct 25, 2016)

I bet that has something to do with your problem.


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## Jasonrkba (Oct 27, 2016)

Does anyone think an exit filter is worth while on this size compressor?


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## Jasonrkba (Nov 1, 2016)

New check valve, same problem. I'm dragging it out of the basement tomorrow and if it still does it I'm getting a cap. I can here the unloader release so I think it's ok.


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## Spring1898 (Nov 1, 2016)

Just a question, but have you already tried it on a separate circuit and a shorter extension cord? Or did we move past that possibility and I just missed it.
Is it oiled or oiless?


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## Jasonrkba (Nov 1, 2016)

I'm doing that in the morning. It is oiless.

Thanks. Jason.


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## Jasonrkba (Nov 2, 2016)

Plugged directly into the wall and it worked like a charm! Guess it was the extension cord.

Thank you everyone who responded to this thread.


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## Marshy (Nov 2, 2016)

Your motor is rated at 14.5 full load amps. In-rush current on motor starts can be significantly higher. The amp draw is compounded because of the extension cord. Glad you found the solution. Remember KISS. Keep It Simple Stupid.


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## Spring1898 (Nov 2, 2016)

You might still be able to get away with a shorter and heavier gauge extension cord. That should mitigate the drop and give you more flexibility


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## Okie (Dec 8, 2016)

I did not read all of this thread:

But to answer your question about what usually causes the motor to lock up and flame out on a electric air compressor is the piston head on the compressor does not unload the pressure off the piston so as the motor can get a running start at a unloaded piston.
You should hear a pist (air spew) immediately when the compressor shuts off when the cutoff pressure switch operates.
If you can bleed off the air pressure from 100 psi to around 25 and it starts ok this tells you it's most likely not unloading.
If you hear air constantly leaking when it shuts off it's the air supply main check valve leaking back to the compressor.
Some cheapo unit use what is called a genie valve, it's a combo check and unloader and it's common for those to fail.

If you do not hear this one time air spew WHEN THE COMPRESSPR RUNS IT'S COMPLETE CYCLE) your UNLOADER is not operating which is usually built into the pressure switch on the small air compressors. You can research such on-line.

Now keep in mind if the compressor is running and gets' up to a pressure of say 80 lbs and it normally cuts off at a higher pressure and you unplug it or it losing incoming voltage the compressor won't unload from the pressure switch unload because it did not complete it's cycle. A genie valve will unload because it sense no air flow and the larger industrial compressors sense when to unload by using a centrifugal unloader built into the compressor PUMP. (anytime the PUMP is not rotating it's in the unload state) This mechanically protects the driver motor from a lock-up seizure.

Summary: Most likely your unloader. Research such online and watch you tube video and read your owners manual.


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## Jasonrkba (Dec 8, 2016)

Lots of good info on this thread. It turned out to to be under amping due to the long extension cord.


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## ncpete (Jan 1, 2017)

Jasonrkba said:


> Plugged directly into the wall and it worked like a charm! Guess it was the extension cord.
> 
> Thank you everyone who responded to this thread.



Rule of thumb with compressors, always use more hose. And never extension cords.


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## Okie (Jan 1, 2017)

ncpete said:


> Rule of thumb with compressors, always use more hose. And never extension cords.



AMEN


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## Jasonrkba (Jan 9, 2017)

Sometimes we learn the hard way, but hopefully others will benefit.


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## jr27236 (Jan 11, 2017)

You didn't learn the hard way. Not only learning about the function of a compressor, you learned about the electrical requirements of it. Before any large electric hungry appliance is installed always have proper electric service to it. Most of older and current wall circuits are 15amp 14gauge wire (with a ground) In you case I believe you said you had two wire (no separate ground) that compressor is rated at pulling 15amps (max capacity of breaker in the box)and not taking into account what else is on that circuit, hence the tripping of the breaker. Rewire your basement walls with 12gauge wire and a 20 amp breaker in the box with 20 amp rated outlets and your problem with safely be resolved. NEVER up a breaker by itself because it trips to cover amperage requirements. Always remember the weak link in electric circuits always has to be the breaker NEVER the wire or outlet or you'll turn it into a glow plug and burn your house down.


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## Jasonrkba (Jan 12, 2017)

Thank you. Great info.


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