air compressor pops breaker

[95PGTTech]

craftsman 919.167320
2 hp 33 gallon, probably 10 years old or more
15a 110v dedicated circuit, been working fine on this for 2 years

problem: motor starts up, runs for about a 2-3 count, then pops 15a breaker.







this winter, the compressor started to not build air pressure (any) even when running constantly. after checking things like the pressure relief and the check valve I decided to take off the rod/piston/head and inspect. Found chunks missing out of the piston ring. Replaced ring, sleeve, and all gaskets. Inspected reed plates and head. Upon putting it back together, problem above started.

I have concluded that it has nothing to do with any aspect of it being an air compressor itself through a series of rule out tests it is a problem with the electrical motor. With JUST THE MOTOR on the bench:

• no switch wired directly to a known good outlet, the problem persists.
• Tried 2 other circuits including a 20a dedicated one just for shits and giggles, same problem although it does run a little longer than a 2 count.
• replaced both capacitors (I was suspecting the run, but just being thorough), no change in result
• tested the small switch inside the cover that breaks continuity between the caps when the cover is off...tests good, if I power the motor without closing the switch the motor hums and never spins (similar to a bad start capacitor).
• the motor spins freely by hand with the power off, there are no unusual noises or binding, and no shaft endplay...there are no visible major breaks in any of the exposed wiring
• measured continuity between the windings...0.3 ohms for each of the three measurements. When testing each winding to ground (motor case) they all show no continuity (infinite ohms).
• I do not have an inline amp clamp to measure how much current the motor is drawing, but I suspect this is the problem since when I connect it to the 20a circuit I get a slightly longer run time before it pops the breaker.
• the centrifugal switch engages inward as the motor spins up, and extends back outward on spindown

I'm at a loss here. I really thought the run cap would do it. An exact replacement was not available. I attached a picture of the original and the replacement specs.

Thank you guys for your time. This one is driving me nuts. Part of me wants to use this as an excuse to go to a 220 compressor, but I don't like saying I just give up and toss it in the trash. It was not doing this problem prior to taking it apart, it was just running forever and not building pressure, and the disassemble/reassemble involved no electrical whatsoever and is on the opposite end of the motor. All I did was unplug the unit from the wall.

 

[DeeKay]

Any chance that's a dual voltage motor and you got some wiring mixed up?
Post up the motor nameplate data.

 

[dogdog]

rotate it by hand first see if anything locking up the compressor / piston ?

 

[95PGTTech]

I don’t believe so
I ordered a clamp on ammeter I love justifying tool purchases. I hope to “prove” the motor has aged and is overdrawing the circuit...or disprove that and have more ammo to suspect a short

 

[95PGTTech]

rotate it by hand first see if anything locking up the compressor / piston ?

The motor and compressor are built together on these cheap units, but I have removed all the “air compressor” aspects of the equation - I am literally spinning an unloaded empty shaft and having the same start run for 2 count and die condition I had with the entire unit assembled. I removed all the controls too, pressure switch etc we are going outlet direct to motor

 

[dogdog]

I think I have the same compressor, and it's been more than 20 years old on occasional operation only...I think they were made by sanborn or something company...

Sorry didn't read all of your statement thoroughly.

reading it again I only notice this.

"the centrifugal switch engages inward as the motor spins up, and extends back outward on spindown"

Just make sure the switch disengages (disconnects the start coil) the start capacitor when it spins up to speed. that is what a centrifugal switch suppose to do. Normal stopped or no rotation it should have continuity...

I don't remember a run cap on mine though. single stage oil-less compressor, super loud.


*****start cap and start coil my bad.

 

[vavet]

It's a little late for this advice, but start with something that bit me a while ago. Plug it into a different receptacle that uses a different circuit breaker. CB's wear out over time and can trip more easily for loads that are near the limit. If it starts and run on a different breaker, then you've found your problem.
I ended up replacing a breaker and it was fine.
My compressor is similar to yours - a C-man oil free, 25 gallon.

 

[Bert_]

Even a 20 amp circuit breaker is problematic for a 2hp motor. 2hp is really best suited for 240v. Some people have been known to run a 1p 30A breaker for this but that's it's own set of issues.

 

[95PGTTech]

It's a little late for this advice, but start with something that bit me a while ago. Plug it into a different receptacle that uses a different circuit breaker. CB's wear out over time and can trip more easily for loads that are near the limit. If it starts and run on a different breaker, then you've found your problem.
I ended up replacing a breaker and it was fine.
My compressor is similar to yours - a C-man oil free, 25 gallon.

Tested it on another 15a circuit in the garage (not dedicated like the compressors is) and a 20a dedicated welder circuit. Same results.

 

[95PGTTech]

Even a 20 amp circuit breaker is problematic for a 2hp motor. 2hp is really best suited for 240v. Some people have been known to run a 1p 30A breaker for this but that's it's own set of issues.

I don’t disagree, but the owners manual calls for a 15a circuit minimum, probably because this thing isn’t 2hp like a lot of them are using inflated sales numbers. Regardless, I have the motor off the unit on my workbench with no load on it.

 

[95PGTTech]

Some more “progress.” I’m not entirely sure it is a centrifugal switch (second pic) because there are absolutely no wires going to or from it and there is a plastic sleeve between it and the motor shaft so it can’t conduct through that. Internally the motor looks slightly worn but fine. No smoking guns. The thermal overload has continuity it’s about 55F in my garage.

When I tested the windings before the thermal overload switch was connected. Now testing the bare windings themselves the values are 1.0, 2.3, and 3.3 which makes a lot more sense. There are no wiring diagrams I can find for this. I forgot to test them to ground I’ll do that after dinner. Can someone please check my capacitor values that’s a little out of my wheelhouse. I researched prior and tried to get the right thing. I can’t imagine this would even need a run cap to stay spinning on a bench unloaded.

 

[dogdog]

****My bad to mention run cap... Most AC induction motor have Start cap, and no run caps..


The second picture does look like a Centrifugal switch or at least the mechanical part of the centrifugal switch.. I think the butterfly thing opens and push against a switch of some sort to open the contacts when it is spinning up to speed... this switch disconnects the start cap. I doubt it is an electronic switch with this motor way back 10+ years and being a cheapie oil-less compressor.

Not sure what the third pic was ..

Keep in mind even though all AC induction motor operates similarly, the components does not look a like... Means they will all have a Run coil(s) and start coil , start cap, centrifugal switch (mechanical or electronic form) and maybe a run cap if motor is large enough.

 

[MoonRise]

Your check of motor coil windings to ground showing infinite ohms (open circuit) is good news. The motor coils aren't shorted to the motor case/ground.

0.3 ohms on the motor windings sounds WAY too low.

Usually should be a few (single digit) ohms.

Sounds like the motor fried itself in the coils.

Also check the CONTACTS for the centrifugal switch. Looks like they are in the black end cap sitting on your bench in Pic #1 in Post #11.

Example testing/diagnosis:

Your Pic #2 in Post #11 is the mechanical portion of the centrifugal switch.

 

[95PGTTech]

Your check of motor coil windings to ground showing infinite ohms (open circuit) is good news. The motor coils aren't shorted to the motor case/ground.

0.3 ohms on the motor windings sounds WAY too low.

Usually should be a few (single digit) ohms.

Sounds like the motor fried itself in the coils.

Also check the CONTACTS for the centrifugal switch. Looks like they are in the black end cap sitting on your bench in Pic #1 in Post #11.

Example testing/diagnosis:

Your Pic #2 in Post #11 is the mechanical portion of the centrifugal switch.

Right, I retested on the bench and got ohms of 1.0, 2.3, and 3.3 which makes a lot more sense. All the testing things I could find said that the two lower should add up to the highest or pretty close. I think I was testing it with the thermal contact still installed so it was reading it as 0.3 in each of the 3 configurations. Just had a chance to run out there and test windings directly to case, and still infinite ohms, which is good, no short to ground.

I will investigate the centrifugal contacts in the morning. there is a switch attached to the inside of that cover but as far as I can tell it doesn't contact the centrifugal switch. one wire from the start cap to the switch to the run capacitor. when depressed, it closes and gives continuity. when not depressed, open circuit. I believe the function of this is to prevent someone from powering on the unit with the rear cover off/ajar. I accidentally once powered it up without depressing the switch and it made a hum noise for a few seconds and popped the breaker (similar to how it would behave with no start cap).

I did play with the mechanical portion of the switch. when it was assembled and the motor would spin up, it would clamp down (move away from the cover). as the motor slowed down and stopped, it would open back up again. Manipulating it by hand it seems to work fine

There was a factory run and start capacitor. pics attached to the first post.

 

[95PGTTech]

Awesome video. I guess that is the centrifugal contacts then. It makes sense now, when the motor is off and the switch is in the OUT position it would depress that switch on the cover and connect the cap to the motor. When the motor spins and the centrifugal switch spins in, it would disconnect the cap from the motor by opening the circuit.

With the cover off I thought this was a simple "cover ajar" switch so I was bypassing it simply by holding it down. I guess to accurately bypass it, I should hold it down for 1 second and then release it when the motor starts spinning.

Edit: maybe the symptoms fit

what happens if the centrifugal switch does not open? "The centrifugal switch should be disconnected at about 70 to 80 % of full speed of the motor if it is not disconnected there will be heavy current continue to flow through starting winding of the motor eventually failure of starting winding and motor, secondly the speed can not reach to its maximum hence the current"

I suppose if it pulls a heavy enough current from never disconnecting, it could pop the breaker. that would explain why it lasts a few more seconds on the 20a circuit. Or maybe I'm just trying to line up the symptoms to fit the thesis. LOL. I'll put humpty dumpty back together and re-test tomorrow when it's not freezing out. That switch inside the cap did have one of the two mounting screws snapped off, but it seemed still very solidly mounted.
Thanks for all the help guys, I really don't like to let **** like this win.

 

[95PGTTech]

Thanks to you guys I have my smoking gun...the contact portion from the centrifugal switch. I got the broken screw out and replaced it, mounted very solid. I believe it is old/worn and it is not making connection (complete circuit) as it should when motor off and first second of start up. All the wiring is inside the cover so I can’t definitively say that, but it behaves just like when I bench test it and DONT depress the switch manually (make complete). I think what is happening is because it’s not complete the motor can’t use the start cap.

With the cover off and on the bench, two new caps, hold switch closed for 1 second and release the motor now starts with good power and remains running until I shut the power off. No abnormal noises grinding or other problems. If I hold the switch closed too long, it starts and dies. If I don’t hold the switch at all I get 1/2 to 1 second of spin with hum and it pops breaker. If I don’t have the caps or switch connected at all and power up the motor there is no result incomplete circuit. Interestingly, apparently the start cap is polarized despite all internet saying no and no markings on cap. Installed one way both the new and old one do the one second then pop breaker installed the other way work fine. I also ended up going back to both old caps I was able to get it to work with them. The new ones are larger and I was going to have to grind the cover to get them to fit and this seemed like a bad idea considering the plastic motor end cover figment is key to mounting this problem contact switch correctly. Regardless, with everything hooked up as tested correctly on the bench all apart with the cover on nice and flush and tight I continue to get the issue I began with. Considering it can be replicated by not completing the circuit with the switch by hand on the bench I’m going to go with it as the problem. I cleaned the contacts super bright the issue must be in the plastic section that contacts the mechanical portion of the centrifugal switch or the copper tabs. I have a feeling this part is going to be obsolete, but I appreciate all the help from everyone.

 

[95PGTTech]

I'm really striking out on this part, craftsman manual and exploded parts diagram don't give any individual motor parts it is serviced as a unit.

I was a lurker on this forum but actually ended up posting here because I searched for a part number that came up with a different thread here of a guy trying to rebuild one so here's some part numbers in case anyone else is searching google hopefully they trip across this thread. it wasn't the caps for me, and getting replacement caps probably wouldn't have worked anyway because of their size difference.

motor d26712 4kcr49tn2450 ax rxfp14
thermal switch cgt36sx klixon
cover switch 958dap217a2c2 0504
cap 24db450370pa

some guy has a used one on ebay right now for 75 + 20 ship. I guess they changed the design because the end cap on his is completely different and the caps are mounted in frog eye type covers on the top of the body. the manufacturer lists a replacement motor (new part number) for 283 plus the case is entirely different so mounting my piston and rod would take some fabrication. I'm striking out bad on this replacement switch. a real shame, it looks like this compressor is going to be junk over what is probably a $5 part but something I can't think up a way to reasonably fabricate a new one of that will work consistently even for my couple time a week usage. Life happens.

 

[dogdog]

They do have electronic centrifugal switches for sell for about $30-ish box, I think...

There was few old thread with links to it. Korean or Chinese or USA.. I think all have them.

dependents on how desperate..

Me.. I would try to bend something back and sand some contacts try and make it work first...

 

[95PGTTech]

They do have electronic centrifugal switches for sell for about $30-ish box, I think...

There was few old thread with links to it. Korean or Chinese or USA.. I think all have them.

dependents on how desperate..

Me.. I would try to bend something back and sand some contacts try and make it work first...

something like this?
https://www.amazon.com/dp/B07KLB862G/?tag=atomicindus08-20

or
https://www.amazon.com/dp/B07XZ9KGKC/?tag=atomicindus08-20

guess it's time to go take a caliper to the shaft. guy on marketplace is selling the same model compressor for $80 because "runs slow". I'll get more details maybe I can make 1 good unit out of 2 dead ones. I really don't want to spend the time running a 220v conduit and line in this garage because I'm getting ready to break ground on a huge detached shop in spring and I want to go really big out there and spend $.

the biggest problem I'm running into is because the contact switch is on the inside of the cover I have to have the entire unit sealed to test it. which means I can't see what's going on in real time or poke tools or multimeter in there to test in real time.

 

[95PGTTech]

Good news. I cut an access hole so I could see mechanically what was going on with the switch. It appeared to be working correctly. I couldn't cut much bigger without getting into the areas on the backside that were needed to mount the switch and the capacitors tight. I then drilled some access holes up top to expose the contacts for the caps. Not touching anything, motor off centrifugal switch in out position (closing the switch), I got continuity. When I closed it (pushed switch inward, opening circuit) I had no continuity. Neither of these were repeatable it was very intermittent. Now having access, I was able to manipulate that metal tab to where it got more and more repeatable and eventually very consistent. I powered up the unit, and it works fine now. Success! Why this decided to happen, or if that broken screw/mount was a part of the issue is up to a power higher than me clearly. All I know is that it's fixed.

I re-installed the sleeve, connecting rod, piston, ring, fan, reed valves, head and intake filter and powered it up. It easily pushes my finger off of the exhaust port on each compression stroke. The very original issue was that the compressor ran forever and did not build pressure so it looks like the diagnosis of bad piston ring and repair is fine. I took some videos but they are too large for the forum to allow me to attach. Shame, it really demonstrates how the switch works in this setup maybe it would benefit someone.

I was going to leave it open like that because the compressor is housed in its own very clean environment but I remembered I had some spare plexiglass and cut a quick piece and attached with a few dabs of 2 part epoxy.

I will follow up when I reinstall this all onto the tank and the controls not my bench rigged ones but I see no reason why I would have further issue. Thank you everyone, you helped me save a compressor. The wife is happy to see something get taken apart for diagnosis and not thrown in the trash LOL. I have two caps and a clamp on ammeter I don't need, but oh well. New tools are always cool. My compressor is in a separate utility shed attached to my garage that is not heated so I will probably wait for nicer weather to reinstall. It's miserably cold out there to be working on cold metal in tight places with no gloves on.

 

[gpiggaz]

Glad you fixed it, I was just about to tell you about this place that I bought a replacement part for a farm duty motor-

https://www.witmermotorservice.com

prices were reasonable and i was able to figure out my motor's problem, I am waiting not he parts to arrive, I think they'll work, but if they don't the few $ I'm out is ok, then I'll go to the electronic centrifugal switch for the $30ish to save a $200 motor on my cement mixer

 

[95PGTTech]

Compressor is all back together in its special little closet and all is working well. It is quite a bit quieter without that piece of missing piston ring and the giant score in the cylinder wall, LOL.

During all of this I must have killed my wifi wall mount switch from popping the breaker over and over during testing. I have power to the switch but not out of it. Jumpered black to black at the switch box and it's all good. This is in a detached shop, so it needs to be on a wifi switch just in case it goes off the middle of the night my wife can just say alexa air compressor off instead of walk outside in the cold and get pissed at me lol.

I'm sure if you multiplied the labor into this x my job hourly rate I would probably have been better off getting a new one on CL or whatever or probably even just a brand new one, but it feels good to see it through and fixed. For the compression rebuild kit and the two caps I didn't need (actually 3 ordered one wrong) and the clamp on ammeter I'm probably over $100. Oh well. Now to get it hooked back up to the hard lines and the shop distribution.

 

[Hingebird]

95PGTTech,

Glad that I found this thread before condemning my compressor for sure. I was ready to turn it into an expansion tank for a new one.

I was able to fix my compressor. Thanks! Same case and fix as yours, but with a motor cover having multiple cracks. This created a condition for the switch making poor contact when closing and shifting it's alignment with the centrifugal switch.

Something to look into as well is ventilation on the motor' cover where the switch is located. While searching for a fix in December, I run into a thread where the compressor was recalled due needing ventilation. Therefore, I drilled holes in the cover following the blank marks on it to complete the repairs.

Thanks,

Conrad

 

[BlackJackJim]

For a typical 2 HP single phase motor @ 110V motor, full load running current is : (746W x 2)/(.85 pf x.7 eff x 110) = 22.79 A. Say 23A.
The minimum breaker size is sized so the 23A is 80% of the breaker rating or 28.75A. It should be connected to a 30A circuit breaker with the branch conductor also rated for 30A, such as 10 AWG Romex.

 

[dnbuckley]

Thanks to you guys I have my smoking gun...the contact portion from the centrifugal switch. I got the broken screw out and replaced it, mounted very solid. I believe it is old/worn and it is not making connection (complete circuit) as it should when motor off and first second of start up. All the wiring is inside the cover so I can’t definitively say that, but it behaves just like when I bench test it and DONT depress the switch manually (make complete). I think what is happening is because it’s not complete the motor can’t use the start cap.

With the cover off and on the bench, two new caps, hold switch closed for 1 second and release the motor now starts with good power and remains running until I shut the power off. No abnormal noises grinding or other problems. If I hold the switch closed too long, it starts and dies. If I don’t hold the switch at all I get 1/2 to 1 second of spin with hum and it pops breaker. If I don’t have the caps or switch connected at all and power up the motor there is no result incomplete circuit. Interestingly, apparently the start cap is polarized despite all internet saying no and no markings on cap. Installed one way both the new and old one do the one second then pop breaker installed the other way work fine. I also ended up going back to both old caps I was able to get it to work with them. The new ones are larger and I was going to have to grind the cover to get them to fit and this seemed like a bad idea considering the plastic motor end cover figment is key to mounting this problem contact switch correctly. Regardless, with everything hooked up as tested correctly on the bench all apart with the cover on nice and flush and tight I continue to get the issue I began with. Considering it can be replicated by not completing the circuit with the switch by hand on the bench I’m going to go with it as the problem. I cleaned the contacts super bright the issue must be in the plastic section that contacts the mechanical portion of the centrifugal switch or the copper tabs. I have a feeling this part is going to be obsolete, but I appreciate all the help from everyone.

I ran across this thread after replacing every easily replaceable part and many hours of looking thru forums that lead me into dead ends. I can tell you, at least for my machine, this was the issue. I was able to repair my compressor in about 20 min. Thank you, thank you, thank you, for saving me an extra $300-500 on a new/used compressor because that's where I was headed if this didn't fix the issue. Many thanks, and good work. All the best.