My compressor motor is not working

[abunaitoo]

So last week I went to turn on my air compressor.
Nothing but a hum.
Tried to turn it by hand and it turns.
Ordered both capacitors.
Came in and same thing.
Took the back off and checked the starter.
Seems to be working.
Cleaned the contact and the flywheel switch.
Still nothing.
Put back the old capacitors and not it jerks while spinning very slow.
It's an old Craftsman 5hp, 220v single phase.
Got it in the 70's.
Any suggestions????

[Baja_Traveler]

Have you tried plugging it into a different circuit? Neighbors compressor had the same problem, turned out the breaker in that circuit was most likely carboned up and would not supply enough start up amperage. Compressor started up fine when wheeled over to my house, so he replaced the breaker in his panel and all was well.

[Noah Zark]

I realize you said you cleaned the centrifugal switch, but what you describe is a switch that's either stuck in the "run" circuit switch position, or not making contact in the "start" circuit switch position, in either case the motor is being energized in the "run" circuit, which doesn't have the torque needed to start the motor and bring it up to speed - the armature will either not turn and the motor hums, or the armature jerks around slowly from pole to pole while humming.

Either the switch is bad, it's missing a spring(s), or it's not shifting positions back to the "start" position (dirt, dried grease, or dust on switch shaft) and closing the
"start" winding contacts and cap to magnetically "kick" that armature over.

Noah

[abunaitoo]

Never thought of checking the outlet.
Stupid me.
Start switch looked like it was OK.
Took it apart to clean and lube it.
Sanded the contacts.

[alfadan]

It may be the unloader valve or "cold start valve" if it has one.
Also if you sanded the contacts, make sure to clean them with alcohol. The grit is insulating and may be keeping the contacts from making up.

[abunaitoo]

I took the belt off, so not the compressor.
Spayed it with some brakeleen.
Outlet seems OK.
240v across, and 110v to ground.
I'm starting to think the motor is just dead.

[bangerjim]

I took the belt off, so not the compressor.
Spayed it with some brakeleen.
Outlet seems OK.
240v across, and 110v to ground.
I'm starting to think the motor is just dead.

DEAD??????????????? FROM the 70's??????????????? 50+ years of service is pretty good!

That's a pretty good life for a motor.

Copper coils do get hot and vibration can break down the insulation and short from layer to layer.

If you have cleaned the starter switch contacts, re-seated all wiring to the motor from the power source I think you better be looking for a new motor. Good news is, 220v 1ø motors are not that expensive, but will not be as "beefy" as the 50 year old one.

Also check the outlet voltage AS THE MOTOR TRIES TO START and see what the voltage drops to. And check the seating of the wires at your breaker box. And while you are at it, buy a brand-new breaker. They go south and can cause problems just like you are having. One of my 220AC unit was giving me fits years ago and it was the breaker.........contacts inside were dirty, corroded, and burnt and did not allow full inrush current (60A) to the compressor motor. Don't try tearing it apart.................just buy a new one!!!!!!

[alfadan]

If it ran but he goes to use it again and suddenly it doesn't, that tells me its a corrosion or connection problem. Also new capacitors dont neccessarily mean GOOD capacitors, especially chinese.

[abunaitoo]

So I plugged in another smaller, 4hp, compressor, and it worked fine.
Guess I'll have to start looking for another motor.
Kind of sad.
It's been giving me good service all these years.
Hate to see it go.
Also have to make a mounting plate.
Everything here cost way more that the lower 48.
Sure wish Lowe's still have Kobalt compressors.

[Mal Paso]

I wish Sears still had blowout sales on what is now 4HP Speedair compressors rebranded Craftsman.

I take solace in my 1400 FTLB Milwaukee battery impact wrench.

So I plugged in another smaller, 4hp, compressor, and it worked fine.
Guess I'll have to start looking for another motor.
Kind of sad.
It's been giving me good service all these years.
Hate to see it go.
Also have to make a mounting plate.
Everything here cost way more that the lower 48.
Sure wish Lowe's still have Kobalt compressors.

If you keep the pulleys and motor speed the same find a new motor with the same amperage rather than hp. My old 2 HP compressor pulled a full 11 amps at 240V, a modern 2 hp would not run that compressor.

[slim1836]

Electricity and I do not get along at all. I’m ignorant on this and rely on others, I let them fix it.

I hope you get the old workhorse up and running.

Slim

[Hossfly]

If you order a new motor be sure to get the correct RPM. I tried 3600 rpm on pump once and it just wont work if you need 1700.

[abunaitoo]

I'm thinking of putting the 4hp motor, from the working compressor, on it.
Same RPM, but I'm sure it will be working harder.
The 4HP compressor needs a new pressure relief valve.
Leaking above 100psi.
It pumps up to 140psi, so is working.
Going to swap only the motor.

[wv109323]

With the belt off spin the motor while it has power on it. See if it will run that way.

[wv109323]

If you get a new motor make it has the correct duty cycle.

[Bulldogger]

So I plugged in another smaller, 4hp, compressor, and it worked fine.
Guess I'll have to start looking for another motor.
Kind of sad.
It's been giving me good service all these years.
Hate to see it go.
Also have to make a mounting plate.
Everything here cost way more that the lower 48.
Sure wish Lowe's still have Kobalt compressors.

Those old motors last decades and turn up in the darndest places, I'd search for one at scrap/recycle first. You might be surprised.
BDGR

[anothernewb]

Don't know if you have one in your area, but that motor can likely be rebuilt for much less than the cost of new. I had a similar issue with my old craftsman compressor. In my case it turned out that the commutator and brushes had started to wear out. less than $100 later and it runs like new.

In my area we a shop that rebuilds motors and the Hutterites communities who also do fantastic work on older electrical gear.

[country gent]

On a compressor that old before investing in a new motor I would think about the condition of the tank, condensation can take a real toll. They are hard to check accurately. The motor on on Dads compressor 5 hp and we replaced it with a new one. About 6 months later the tank developed some pin holes around where the feet were welded on. While it would pump up it wouldnt hold for long.

Then there is the pressure valve regulators and plumbing thats all 50 years old. Even the old compressor is 50 years old and may be in need of some work on reed valves and other components.

[abunaitoo]

With the belt off spin the motor while it has power on it. See if it will run that way.

I did try that.
Though, maybe, only the start was not working.
No luck.
Unless I just didn't spin it fast enough.

[abunaitoo]

Don't know if you have one in your area, but that motor can likely be rebuilt for much less than the cost of new. I had a similar issue with my old craftsman compressor. In my case it turned out that the commutator and brushes had started to wear out. less than $100 later and it runs like new.

In my area we a shop that rebuilds motors and the Hutterites communities who also do fantastic work on older electrical gear.

I've taken another motor to the only motor rebuilder I could find here.
It was from an old Atlas lathe.
Seemed like they didn't know what to do.
Just looked at it and said I needed a new motor.