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Forum topic by bilyo posted 02-08-2018 01:57 AM 392 views 0 times favorited 13 replies Add to Favorites Watch
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bilyo

125 posts in 1007 days


02-08-2018 01:57 AM

I have a Ridgid OF4515A 4.5 gal twin tank compressor. I was using it today and it lost pressure and stopped. After it cooled down I tried to start it again, but the motor just hums. I suspect one or both of the motor capacitors, but I don’t know if failure while running is their method. Could it be something else? If it is the capacitors, should I find out which it is and just replace it or just go ahead and replace both?


13 replies so far

View Lazyman's profile

Lazyman

1688 posts in 1292 days


#1 posted 02-08-2018 05:42 AM

I think that humming is one of the symptoms of a bad capacitor. It looks like it has both a start and a run capacitor. You can try testing the capacitors with a multimeter.

When you said it lost pressure, do you mean suddenly? If so. maybe the cylinder seized up? Not sure if there is an easy way to turn it by hand?

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View Loren's profile (online now)

Loren

9947 posts in 3552 days


#2 posted 02-08-2018 05:47 AM

If you’re using it on an extension cord, that
can prevent the motor from starting when
the tank is pressurized.

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bilyo

125 posts in 1007 days


#3 posted 02-08-2018 06:42 PM

I found some info on line on checking capacitors. Resistance check on both capacitors shows infinite resistance between the two posts. Based on that, the capacitors are good (according to the instructions). My meter won’t do a capacitance check. Not sure it that is necessary or if the resistance check is definitive.

I took the fan cover off and, using the plastic fan, I can turn everything freely clockwise (looking from the fan end). However, if I try rotating counterclockwise, something stops it at the 11:00 position. I don’t know what it’s normal rotation direction is, but I don’t think it is normal to have a motor blocked in one direction. Is it?

Also, the fact that it turns so easily clockwise is concerning. The piston is moving normally and, it seems to me that I should be getting some resistance on the compression stroke.

View Holt's profile

Holt

226 posts in 2533 days


#4 posted 02-08-2018 07:58 PM

Those caps are probably decent sized electrolytic (looks like a can and has the polarity marked on one side. If so and your ohm meter is analog, with cap out of circuit, short the two leads to make sure it is discharged. Then put the red lead on the plus side, black lead on the other while you watch the meter needle. It should swing up towards zero ohms then quickly fall back towards open circuit. That would actually check it’s operation as a cap…


I found some info on line on checking capacitors. Resistance check on both capacitors shows infinite resistance between the two posts. Based on that, the capacitors are good (according to the instructions). My meter won t do a capacitance check. Not sure it that is necessary or if the resistance check is definitive.

I took the fan cover off and, using the plastic fan, I can turn everything freely clockwise (looking from the fan end). However, if I try rotating counterclockwise, something stops it at the 11:00 position. I don t know what it s normal rotation direction is, but I don t think it is normal to have a motor blocked in one direction. Is it?

Also, the fact that it turns so easily clockwise is concerning. The piston is moving normally and, it seems to me that I should be getting some resistance on the compression stroke.

- bilyo


-- ...Specialization is for insects.

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MrUnix

6339 posts in 2103 days


#5 posted 02-08-2018 08:10 PM

Those caps are probably decent sized electrolytic (looks like a can and has the polarity marked on one side. If so and your ohm meter is analog, with cap out of circuit, short the two leads to make sure it is discharged. Then put the red lead on the plus side, black lead on the other while you watch the meter needle. It should swing up towards zero ohms then quickly fall back towards open circuit. That would actually check it s operation as a cap…
- Holt

Correct – except they are not marked for polarity (it is an AC circuit). If all you get is an open circuit (infinite resistance) – then the capacitor is fried. Same deal if all you get is zero resistance (short). You should see a swing from low to high resistance. Swap leads and you should see the same. Do it a couple of times to make sure. If not – it is most likely fried.

Cheers,
Brad

-- Brad in FL - In Dog I trust... everything else is questionable

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bilyo

125 posts in 1007 days


#6 posted 02-08-2018 08:37 PM


Correct – except they are not marked for polarity (it is an AC circuit). If all you get is an open circuit (infinite resistance) – then the capacitor is fried. Same deal if all you get is zero resistance (short). You should see a swing from low to high resistance. Swap leads and you should see the same. Do it a couple of times to make sure. If not – it is most likely fried.

Cheers,
Brad

- MrUnix


Correct. With an analog meter, the reading on one cap goes almost to 0 and slowly (maybe count to 3 or 4) comes back to infinity. The reading on the other cap jumps about 1/2 way up scale and then quickly falls back to infinity. Same for swapped leads.

View Bill1974's profile

Bill1974

124 posts in 2889 days


#7 posted 02-09-2018 08:46 PM

You should be able to spin it in either direction. To feel compression you would need to plug or restrict the outlet port on the compressor head. There should not be much if any difference in the feel either in either direction.

Other things that could be bad, the start switch or the start winding. there should be an access plate on the rear end of the motor. If it’s not a start switch or a capacitor, look for a new compressor. On the plus side almost anything else is quieter (I think I have the same one).

How many hour do you think you have on it?

View bilyo's profile

bilyo

125 posts in 1007 days


#8 posted 02-09-2018 10:18 PM

Bill1974,
You are correct. It is a noisy critter. I don’t know how many total hours it has. I bought it used a few years ago and I haven’t put many hours on it: just occasional tire filling, spraying, etc.

Since my OP, I have taken the compressor head off and found nothing alarming. following that, I removed the motor and took the rear (opposite the compressor pump) end cover off. The bearing runs smoothly and I found no broken or loose parts. I see nothing that could have stopped the armature from turning. I put the cover back on and it now turns freely in either direction. Go figure!

I’ve got to make some new gaskets for the compressor pump. Once I get it back together, I’ll try to test run it. I’ll let you know what happens.

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bilyo

125 posts in 1007 days


#9 posted 02-11-2018 03:32 AM

It is all back together. The motor rotates freely in both directions by hand. Plugged it in, flipped the switch, and the motor rotated about 1/2 turn and stopped and hummed. But it’s not a hard stop. It just stops rotating and hums. If I flick the cooling fan, it will rotate maybe another 1/2 turn and stop and hum. Does that mean that one of the caps is indeed bad? How do I tell which one? My meter will not test capacitance.

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bilyo

125 posts in 1007 days


#10 posted 02-13-2018 10:52 PM

I found a local motor repair shop that checked the two caps and found that they are OK. That left me scratching my head. So, I thought I would give one more look inside thinking that there might be something amiss with the run switch mechanism. This time, when I took the rear end plate off, the armature came with it which should not have happened. The armature shaft has sheared off at the bearing at the pump end. It sheared off in such a way that when it is not under load the two pieces stayed in alignment. This allowed the the whole shaft and armature to rotate freely when turned by hand, but not under load. So, the motor is ka-put.

A new California Air Tools compressor will be delivered Thursday.

Thanks for all the help and advice.

View fivecodys's profile

fivecodys

909 posts in 1540 days


#11 posted 02-13-2018 11:00 PM

California Air makes a real nice compressor.
I bought one here at work to use on our laminator and does a great job and it is pretty quite too!

-- The less an idiot knows, the louder he seems to know it!

View 01ntrain's profile

01ntrain

237 posts in 974 days


#12 posted 02-13-2018 11:52 PM

Good to know. I’ve got the same compressor, that I use on the jobsite.

View bilyo's profile

bilyo

125 posts in 1007 days


#13 posted 02-14-2018 03:51 AM

Thanks for the good word about California Air. I was buying it kind of blind. My decision was based mainly on its low noise rating and negative comments about others of the size I wanted. The worst comments I’ve read about CAT is regarding shipping damage on arrival due to poor packing.

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