# Air compressor runs very slow and trips breaker



## Balln2894 (3 mo ago)

I have a craftsman’s air compressor that has ran great always until the other day. I went to turn it on and now it’s runs noticeably quieter than normal and real slow. Very sluggish. It runs for about 1 minute and then trips the breaker at my house and shuts off. Any ideas? Thank you everyone


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## sledman8002002 (Jan 28, 2021)

Balln2894 said:


> Very sluggish


Being that its sluggish my first thought is possibly a motor bearing(s) is seizing.


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## stevon (Mar 5, 2019)

Balln2894,

A failed bearing usually is pretty noisy when running or locks up the motor. with power disconnected roll the compressor and pump belt to feel for any unusual resistance. I think a start capacitor or the start clutch switch is your problem. Do you have a volt meter to test those parts? A bad check valve can cause slow start up but it wouldn't necessarily trip the thermal overload or circuit breaker. What is the FLA (full load amps) listed on the motor? Are you near that at startup after the first second or two? an ammeter comes in handy trouble shooting problems. a few pictures and model name would be helpful

Stephen



Balln2894 said:


> I have a craftsman’s air compressor that has ran great always until the other day. I went to turn it on and now it’s runs noticeably quieter than normal and real slow. Very sluggish. It runs for about 1 minute and then trips the breaker at my house and shuts off. Any ideas? Thank you everyone


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## Balln2894 (3 mo ago)

I spun the motor by hand I don’t feel any resistance, I do have a voltmeter, but I’m not sure how to get to the start capacitor and check it. How many volts am I looking for? And yes I agree with you I don’t thinks it’s. A bearing because the motor is much quieter than its normal operating noise and it’s very slow to run , doesn’t make any air pressure and after about a minute of running it will trip the breaker. I will attach pictures of the compressor. Thank you for trying to help me, I don’t know much about compressors


























stevon said:


> Balln2894,
> 
> A failed bearing usually is pretty noisy when running or locks up the motor. with power disconnected roll the compressor and pump belt to feel for any unusual resistance. I think a start capacitor or the start clutch switch is your problem. Do you have a volt meter to test those parts? A bad check valve can cause slow start up but it wouldn't necessarily trip the thermal overload or circuit breaker. What is the FLA (full load amps) listed on the motor? Are you near that at startup after the first second or two? an ammeter comes in handy trouble shooting problems. a few pictures and model name would be helpful
> 
> Stephen


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## stevon (Mar 5, 2019)

Balln2894, 

instructions on testing a motor capacitor:



how to test a start capacitor with a multimeter - Google Search


and:





instructions on testing the motor windings:






Stephen


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## stevon (Mar 5, 2019)

Balln2894,,

Also an article about testing a single phase motor:









How To Test and Check Single phase Electric Motors


Single phase motors test, insulation resistance,




www.electricalengineeringtoolbox.com




.


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## stevon (Mar 5, 2019)

Balln2894,

My $.02

You have an "oil free" compressor, they are basically a cheap, light duty consumer grade "throw away" type model. Your problem sounds like a motor issue. For most folks that's what they do (chuck it) when the cylinder starts giving them problems (and it will). The only reason you would try to fix this compressor is:

A. you are bored and have nothing else to do
B. you are technically savy (electrical Engineer) and love a challenge or
C. You are just that dam cheap

For $50 on craigslist you could find a 1.5 HP 120 volt replacement compressor (recommend an oil type) with a lot less work involved IMO

Stephen


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## stevon (Mar 5, 2019)

Balln2894,









a replacement pump/motor alone is up to $300
part number E105180SV replacement pump





Craftsman 921.164710 Parts - Master Tool Repair


Get Craftsman 921.164710 Parts at Master Tool Repair. Our site is easy to shop and we have online schematics, tech docs and videos available.




aircompressorpartsonline.com





Stephen


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## afacademydad (1 mo ago)

Two things go together here. 1) compressor runs slow and 2) It trips breakers.
Sounds to me that there is too much of a voltage drop, thus pulling too much current (amps). Sounds like it's on a circuit with a LOT of other things plugged in and running on it. Or you're running on a thin extension cord. You say it's been running great until recently. Is it possible that some other things got plugged into that same circuit that the compressor is on?

What you need to do is figure out all the things that are on that circuit; temporarily disconnect everything; and measure the voltage at the outlet you plug your compressor into. Should be somewhere around 120-125vac. Then, with only the compressor running, in the 2nd outlet of that receptacle check the voltage again while the compressor is running. It's normal to lose a couple volts; but if you're losing like 5 volts or more, e.g. it's reading 115vac, then that's a pretty big voltage loss.

Could be the compressor is pulling 13, 14, 15 amps on 14 gauge 15 amp wiring and you're maxing out the circuit's capabilities. Or if the circuit and wiring are big enough and you don't have a major voltage drop unless you have all other things plugged in too, then you could possibly just have too many things working on that circuit at the same time.

Until I put in a dedicated 240vac and dedicated 120vac circuit for my welder and plasma cutter, when I used either previously in the garage, I had to unplug the chest freezer and refrigerator in the garage so I didn't have too much running. Also, when my compressor was on a 50 foot extension cord, the voltage dropped from 124 to 115vac when the compressor was on. When I changed out the 14 gauge 50 foot extension cord with a 12 gauge 25 foot extension cord, the voltage drop when the compressor was running dropped from 124 to 120vac. MUCH Nicer. When voltage goes DOWN.... current (AMPS) go UP. Breakers are sensitive.

Mike


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