Compressor Motor Issue

[Chris129]

Hi to every one, I am new to this forum and I have a question. I have a compressor motor that slows down and stops under load and blows the circuit breaker. I have tested the start and run capacitors and they checked good. Now for the kicker, when I remove the air line from the compressor that feeds the tank. It runs fine until I put cover port on the compressor that feeds air to the tank. Then the motor will act up again. The compressor turns by hand fine.

 

[jrsulo]

Check valve

 

[walta]

Are you using the factory motor and pulleys?

Do you have a clamp on amp meter? If so is the motor pulling over its rated amps?

Do you build any pressure in the tank before the motor stalls?

When you say the “circuit breaker blows” is that the breaker on the wall or the overload on the motor?

Is the unit plugged into an extension cord or into the wall?

Is the circuit breaker for this outlet 20 amps?

What is the HP rating of the motor?

Walta

 

[jhelrey]

Mine did it... Use a blow gun and spray out the back of the motor. Brushes were dirty and not making contact. Known issue when I Googled my model number of motor.

 

[redmondjp]

Mine did it... Use a blow gun and spray out the back of the motor. Brushes were dirty and not making contact. Known issue when I Googled my model number of motor.

Are you sure that your motor has brushes in it? Most compressor motor are induction motors which don't have brushes - maybe you are thinking of the centrifugal start winding cutout switch?

 

[nadogail]

Does the compressor build pressure in the tank?

 

[gungatim]

LGR

 

[jhelrey]

Are you sure that your motor has brushes in it? Most compressor motor are induction motors which don't have brushes - maybe you are thinking of the centrifugal start winding cutout switch?

I'm not sure exactly what it was as this was many years ago. I just remember pulling the rear of the motor apart, removing debris with a brush, and air hosing things off. Motor started much quicker than it had before.

 

[Chris129]

Hi Walta, Sorry for the delayed response, I have a bad time getting back on this forum. Now to your questions. 1 Yes I am using everything original. 2 No I do not have a clamp on meter. 3 Yes, it does build some pressure in the tank. Both circuit breakers some times but mostly the thermal breaker. 4 No, no extension cord is used. 5 It is a 20amp breaker. 6 It is 2hp motor. PS. When it does run it looses it's torque and slows down, that's when it pops the breaker.

 

[Chris129]

Hi red, No I am not sure if it has brushes

 

[Chris129]

Hi jherlrey, Tried what you suggested, no luck

 

[dogdog]

Hi to every one, I am new to this forum and I have a question. I have a compressor motor that slows down and stops under load and blows the circuit breaker. I have tested the start and run capacitors and they checked good. Now for the kicker, when I remove the air line from the compressor that feeds the tank. It runs fine until I put cover port on the compressor that feeds air to the tank. Then the motor will act up again. The compressor turns by hand fine.

I don't think you have electrical motor issue if you are able to run the compressor with no load....

Maybe a check valve or some sort of unloader issue ...

Not sure what compressor you have, if it have start / run capacitors it is probably a bigger unit...

un hook the belt from the motor and compressor and see if the motor runs for a while like > 5 minutes... if it does, then probably you should focus on the compressor or check valve un-loader valves....

 

[Chris129]

Hi nad, Yes, it will build some pressure before it starts to slow down and stop.

 

[Chris129]

Hi dogdog, Checked the check valve it is OK, The fact that I can put my finger over the air fill port and stop the motor says that there is something wrong with the motor. It should blow my finger off the fill port but instead it slows the motor down and pops a breaker. Yes it has start and run capacitors both check good.

 

[Wrench97]

Check valve will not be an issue when the motor is already running only for starting once there is air in the tank.

My next step would be to check amp load while running and the oil level in the compressor but it sounds like the motor may be failing.

 

[The Cobbler]

if you can stop the motor with your finger making pressure , it is probably toast .

unless you want to try a run cap just incase

 

[LX-Markham]

Is this a new issue? Did it run fine before?

Maybe not the case, but sounds like what happened to mine. I bought a used compressor. Tested it before I bought it, it worked fine. Plan was to renovate the garage and install it after the reno. When it came time to plug it in ran as you described yours. Would run, then slow down, then blow the motor breaker.
Turns out the electrician hooked up the 240 outlet wrong and I was trying to run the compressor on 120.

 

[The Cobbler]

^^^ good point !

 

[dogdog]

Hi dogdog, Checked the check valve it is OK, The fact that I can put my finger over the air fill port and stop the motor says that there is something wrong with the motor. It should blow my finger off the fill port but instead it slows the motor down and pops a breaker. Yes it has start and run capacitors both check good.

Check valve will not be an issue when the motor is already running only for starting once there is air in the tank.

My next step would be to check amp load while running and the oil level in the compressor but it sounds like the motor may be failing.

I think the OP stated that the motor will run as long as there is no load on the compressor... unless I mis-interpert it twice. Unhook the belt will isolate it from the compressor I think..

Maybe turning the manually compressor with hands once the belts off and see if you can stall it the same way covering the port ? Not too sure how to test or stall a AC motor.... safely

 

[NETexas]

I have a 30 year old Sears 2hp 220vac compressor I bought new. It worked fine one day and tripped wall breaker the next. I changes the capacitor and same thing ( should has checked it). Removed belt and motor tripped again. Started looking for a new motor until I saw the price. Pulled motor apart and a dirt/Mud dauber had built a nest next to the contactor, only allowing one leg of 120vac to motor. Removed nest and cleaned contacts with diamond fingernail file and is back in service.


Sent from my iPad using Garage Journal

 

[walta]

I like photos let’s see a few compressor, motor, pulleys and motors tag.

Your symptoms do sound a little like a motor configured for 240 volts being feed 120.

A clamp on amp meter will tell us a lot about if the motor is overloaded.

This is Garage Journal if you don’t own a tool the obvious solution is go buy the necessary tool.

https://www.harborfreight.com/digital-clamp-meter-96308.html

Walta

 

[dogdog]

I have a 30 year old Sears 2hp 220vac compressor I bought new. It worked fine one day and tripped wall breaker the next. I changes the capacitor and same thing ( should has checked it). Removed belt and motor tripped again. Started looking for a new motor until I saw the price. Pulled motor apart and a dirt/Mud dauber had built a nest next to the contactor, only allowing one leg of 120vac to motor. Removed nest and cleaned contacts with diamond fingernail file and is back in service.


Sent from my iPad using Garage Journal

Sometimes tighten the belt to much on equipment will cause unnecessary load on motor and components. They are suppose to have some slack. Dunno about the OP's situation. It is always easier to isolate the components troubleshooting weird issues like this.

 

[Chris129]

Hi Cobbler, Don't know what a cap test is.

 

[The Cobbler]

"try a run cap" sorry, I mean try replacing the run capacitor , even tho it tested fine.

 

[Chris129]

Hi LX, Yes this is a new issue. Was running fine when I put away last year.

 

[Chris129]

Hi walta, The motor will run on 240v or 120V. The motor is wired for 120V's. Ran good last time I used it.

 

[Chris129]

Hi JH, No brushes in mine, it is a induction type motor

 

[dogdog]

Hi JH, No brushes in mine, it is a induction type motor

There is not much to an induction motor... Either separate, test the components and isolate the issue, or throw parts at it. and the troubleshooting starts from separating your compressor from your motor which is linked by a belt.

If you still think it is the motor....

I am not sure what you used to test those capacitors... hopefully it's an ESR type meter that can accurately test the values... other than the ones on a multimeter. Something about measuring capacitance on a capacitor with esr, pretty sure you can google it, it was a thing popular by Samsung.

 

[Chris129]

Hi dogdog, I tested them using a FLUKE 175 true rms multimeter. Both capacitors tested good. Have disconnect the motor from the compressor and ran the motor. Appeared to run OK. hooked it hack up to the compressor, disconnected the fill line (line from the compressor to the tank) ran the motor again and put my finger over the discharge out let on the compressor and I could slow the motor way down, until it popped the breaker. PS Some people have mentioned a unloader valve. Checked my compressor and it don't seem to have one. My big compressor does however.

 

[dogdog]

Hi dogdog, I tested them using a FLUKE 175 true rms multimeter. Both capacitors tested good. Have disconnect the motor from the compressor and ran the motor. Appeared to run OK. hooked it hack up to the compressor, disconnected the fill line (line from the compressor to the tank) ran the motor again and put my finger over the discharge out let on the compressor and I could slow the motor way down, until it popped the breaker. PS Some people have mentioned a unloader valve. Checked my compressor and it don't seem to have one. My big compressor does however.

If you have the belts off and motor runs fine and strong... and with belt on compressor slows significantly after some pressure is build up pressure at the discharge port. I would think it's some problem with the compressor, and less likely to be the motor though. I don't have any safe and creative ideas how to test the motor under load without the belt on, unsafe would be like a piece of wood (2x4) on the pulley as resistance to the load. Those thing scares me. Unless you have another motor to go in there and test.

Maybe post the make model of your compressor, maybe some one knows. I don't have big compressor in my shop.

as far as capacitor reading, as far as I know... sometimes multimeter reads capacitance... but there was a time period that ESR was popular in capacitors when those Samsung TV started to die because of bad capacitor in the their power supplies.. I dunno what happened to it since. There are plenty of topics about this on capacitors in electronic forums. So if you still think it's the motor, the Run Capacitor would be parts I throw at it as mentioned earlier by another poster.

 

[Wrench97]

I would think just the opposite, motors will run fine with no load but once a load is applied it slows down I would think motor issue.

 

[marinusdees]

Induction motors run at a fixed rpm controlled by the alternating current at 60 cycles per second, and don't slow down under load, unless it's overload in which case they trip the breaker and/or run hot , but not for long.

 

[73project]

Do you have a motor service shop in your area? Take that motor down to them and have them load test it. They will be able to tell you if your motor is performing correctly, or if there is a problem. Most motor service/rewind shops will test your motor for free. You dont want to guess and start throwing parts at the problem, because that's the most expensive way to find the issue.