Air Compressor puzzle

[Redneck in training]

Here are some pics: First the meter as set on Ohms. I grounded the black lead to the green wire in the motor first. I then touched the output wire from the start capacitor. Nothing or no needle movement. I then touched the black wire with the red meter lead while meter was grounded. Nothing. I then touched each run capacitor wire while meter was grounded. Nothing. I then touched the two run capacitor wires and the needle went to zero. I then touched the green wire and the motor casing: the needle went to zero. All other touches needle stayed on infinity.

That means that the winding of the motor is not shorted to the ground. That is good. When you touch the capacitor wires you are measuring resistance of the winding that is parallel to it. It is typically some small value. To get more precise measurement you need to adjust zero fo your meter. Short the leads and use screwdriver to adjust the needle to zero. Then use the smallest range to measure the resistance. it should be around 10-20 ohms. Make sure both capacitors are good, the starting switch is closed and the power cable and plug are also good. If it still doesn't start it is time to take it to a repair shop. They have a tester that can detect bad winding and even might have used motor if your is bad beyond repair. And Moss Road is right if the unload valve on the compressor is bad the motor will not develop enough torque to start running and it will blow the breaker.

 

[arrow]

That means that the winding of the motor is not shorted to the ground. That is good. When you touch the capacitor wires you are measuring resistance of the winding that is parallel to it. It is typically some small value. To get more precise measurement you need to adjust zero fo your meter. Short the leads and use screwdriver to adjust the needle to zero. Then use the smallest range to measure the resistance. it should be around 10-20 ohms. Make sure both capacitors are good, the starting switch is closed and the power cable and plug are also good. If it still doesn't start it is time to take it to a repair shop. They have a tester that can detect bad winding and even might have used motor if your is bad beyond repair. And Moss Road is right if the unload valve on the compressor is bad the motor will not develop enough torque to start running and it will blow the breaker.

I don't think my meter has the capacity to measure "small ranges". Both capacitors are good. Cable and plug look to be fine.

If there his no air in the tank and the bottom moisture let off fitting is open, and the compressor piston turns freely by hand, would this cancel out a problem with an unloader valve ?

Allow me to ask another question at this time that may have been lost in this shuffle. I measured the start cap with a capacitance meter a friend has. It read 141. The label on the cap states a range of 136-163. This cap if good, should have still started this compressor correct? Even though it was more speccing toward its lower number Mf's, it should still be adequate?


There is still one more thing i can do and that is to dissemble the motor from the air valving and then see if the motor starts. This is a pain the the ***** job as I have already stripped a hard to get at Torx screw head deep in the covering.

 

[Redneck in training]

I don't think my meter has the capacity to measure "small ranges". Both capacitors are good. Cable and plug look to be fine.

If there his no air in the tank and the bottom moisture let off fitting is open, and the compressor piston turns freely by hand, would this cancel out a problem with an unloader valve ?

Allow me to ask another question at this time that may have been lost in this shuffle. I measured the start cap with a capacitance meter a friend has. It read 141. The label on the cap states a range of 136-163. This cap if good, should have still started this compressor correct? Even though it was more speccing toward its lower number Mf's, it should still be adequate?


There is still one more thing i can do and that is to dissemble the motor from the air valving and then see if the motor starts. This is a pain the the ***** job as I have already stripped a hard to get at Torx screw head deep in the covering.

There are two capacitors. Both have to be good for the motor to start. 141 mF should be good. Empty tank is equivalent to unloaded compressor.

 

[Raspy]

arrow, it's not your unloader valve because the first time it happened you said the there was no pressure in the tank.

But if it was later trying to start against full pressure it would probably have the same symptoms you describe; blowing the breaker. I had one that would not start on anything less that a #12 cord and only then if it was a short one. Otherwise it would turn very slowly for a couple of seconds and blow the breaker or trip the reset on the compressor. Compressors these days seem to be designed to need every amp they can get to just barely get started.

It would be funny if your house happened to have #14 wire on the 20 amp circuits and that particular circuit was a very long run, or even with another load along the way.

 

[arrow]

arrow, it's not your unloader valve because the first time it happened you said the there was no pressure in the tank.

But if it was later trying to start against full pressure it would probably have the same symptoms you describe; blowing the breaker. I had one that would not start on anything less that a #12 cord and only then if it was a short one. Otherwise it would turn very slowly for a couple of seconds and blow the breaker or trip the reset on the compressor. Compressors these days seem to be designed to need every amp they can get to just barely get started.

It would be funny if your house happened to have #14 wire on the 20 amp circuits and that particular circuit was a very long run, or even with another load along the way.

Your symptom sounds just like mine. I have #10 going out to the garages for 75' or so. This thing worked fine in the exact same place on its own circuit since 2004. It is under some mysterious load that makes it fail to get going.

 

[Xfaxman]

First the meter as set on Ohms. I grounded the black lead to the green wire in the motor first.

For AC wiring Black is "hot", White is "neutral" and Green is frame ground.

Part of your testing proved nothing is shorted to ground.

You need to test continuity through the starting switch and aux winding.

 

[Zerk]

If its blowing breakers, that's an overload. Bad caps would probably just cause it to sit there and hum the motor, not trip the breaker in 3 seconds.

So I gotta ask a couple questions, and please forgive me if they've already been asked. I worked in I.T. for 25+ years and the first thing you learn doing help desk support is that while you don't have a clue what the person needing help's knowledge level is, they'll get irked if you ask them questions below their knowledge level real quick. :laughing: So here goes...

Did the compressor ever work?
Did it work one day, then start blowing breakers the next time you tried to use it?
Is there any air pressure in the tank?
Have you tried bleeding off all the air pressure and trying it again?
There's a pressure switch and there should be an unloader in that pressure switch. If its not unloading (bleeding off the air pressure in the area between the compressor and the tank), it can cause enough pressure that the motor can't spin. Bleeding off the tank of all air pressure will let you skip by a bad unloader to test that theory.
Have you tried disconnecting the compressor from electrical power and turning the motor by hand?
Does the motor turn freely?
Have you tried disconnecting the motor from the compressor and turning the compressor by hand?
Does it turn freely with no air pressure built up?
I think I read you changed the caps...
Were there two caps or one cap?
Test one/both caps while they are disconnected from everything else.
If they appear to take and hold a charge, they are probably good.

If the pressure/on-off switch is good...
And the unloader is working...
And there is no air pressure in the tank...
And the capacitors check out good...
And you can spin the motor by hand easily...
And you can spin the compressor by hand easily...
And it still blows the breaker after it's turned on after a couple seconds....
Then the motor is suspect and probably has an internal short.
Pull the motor and take it to a local motor repair shop and ask them to bench test it if it doesn't cost too much for peace of mind.

Here's a link to a really good troubleshooting guide.... hope it helps.
LEESONｮ Electric | Motor Trouble-Shooting Chart

Thats is a great list.

for little motors, that were not worth repairing, if it spun, we said windings bad, if not bearings. I don't have much experience with caps though. I got three compressors and none have them. Old fashioned style with oil and belt.



If there is a pulley you can turn over, you should air coming and going too. it could be some something else causing the problem.


Also I would ask how long it runs for. Is there enough to time to get a clamp on amp meter on it? Start up is high



Has anybody mentioned taking the motor into a motor shop to be tested? I am not sure how easy they are to find. Used to be around.


Have you tried running with air out take disconnected? Don't do this long and be ready to shut off. I am not sure if it will over speed without load.


As said ohming the winds is probably a real good start. Out of curiousity I would google the cost of a new motor, just to see if it is worth just chucking one in and being done with that piece of the puzzle.


Lots of people build air compressors, couple of mine are home made I got out of from someone else. So you may found lots of discussion on how they work. Most people I don't think build oiless ones though. Noisey and cheap.

 

[Zerk]

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It would be funny if your house happened to have #14 wire on the 20 amp circuits and that particular circuit was a very long run, or even with another load along the way.

But it was working, I thought.


Over 75 feet, you should up size wire. But the compressor may not actually be running full rated amps for the wire.

Having 14 on 20, is not likely to cause a trip, unless a long run, and have a voltage drop. It is more a matter of safely sizing the wire.

Myself, in my garage, I use 14 for lights and 12 for outlets. I like seperate circuits so you are not left in the dark, and if you need to work on lights you can plug a light in outlet. I probably go a little over board for circuits.

 

[Zerk]

For AC wiring Black is "hot", White is "neutral" and Green is frame ground.

Part of your testing proved nothing is shorted to ground.

You need to test continuity through the starting switch and aux winding.


View attachment 504148

Only if it is 120V, not 240V. If 120, you shoud check outlet polarity. Though neither here not there.

But 120, white and green are bother going to read to ground in outlet, but not at the motor. 240V the white will be 120 to ground. I didn't catch if this 120 or 240.

 

[arrow]

For AC wiring Black is "hot", White is "neutral" and Green is frame ground.

Part of your testing proved nothing is shorted to ground.

You need to test continuity through the starting switch and aux winding.




View attachment 504148

So where do I place the meter rods? One on switch and black to ground? Thanks