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OT - AC Fan motor problem

I don't know what other group to post this in, but this the kind of group where I'm likely to find an answer. If it weren't Saturday afternoon, I'd call the motor shop.

1/3 HP 220 V 1.2 A 1120 RPM motor for the fan which blows air over the coils in the outside AC unit. It's started by a capacitor which sits in the control box. There are 3 connectors on the capacitor, and I can read 5 uF on part of the can. There's no switch to cut the capacitor in and out, so I assume it's a run capacitor that's always in the circuit. Three wires run into the motor.

Briefly, it will turn very slowly. If it give it a push with a stick, it will turn a round or two and then slow down to a creep again. Some times it will start and run.

Now for the full story.

About two years ago the motor quit running - on a Friday night - typical. It wasn't the capacitor then, and I wound up at a small motor shop. I don't know what the recommendation was, but I think the proprietor felt that it just needed lubrication. I took it apart and oiled the packing material and after reassembly, it ran again.

It quit again Friday, two years after the original repair. This time I figured it was time for a new motor. The repair shop was open Saturday AM and the owner took it apart and felt that the bearings weren't bad, but that the retainer disk wasn't holding the front (self centering?) sleeve bearing in place correctly. I had that apart 2 years ago, so I probably was the culprit there. He also felt that there was more end play than he expected, so he put two more plastic washers in the front end. There was still a good deal of end play, but less than before. He relubed the packing around the bronze sleeves and reassembled the "front" bearing where the retainer had come loose. He "shook" the shaft and didn't feel any significant side play. It turned without difficulty. No scraping sounds. He would have tested it but he would have had to cut the plastic connector off to do that, so he sent me on my way with the motor to see how it worked. He did check the capacitor on a meter and he said it was ok.

Some times it will start and run at full speed, other times it just turns slowly and won't get any faster. Same symptoms as before the relube. There is more end play in the motor than I'd expect, but there was a lot for the past two years also.

Any ideas on what's wrong and how to fix it?

If I have to replace the motor, he's got a 1/2 HP motor of the correct frame diameter, but we didn't look to see the amperage. Any reason not to go up to 1/2 HP if the amperage is just a little higher?

TIA RWL

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Reply to
RWL
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"It's Dead, Jim."

One of the windings is probably intermittent open - it's a capacitor run motor, there is no start switch. Stick a fork in it, it's done.

I wouldn't have even bothered to crack the motor case the second time, they're not worth the effort. You can get new motors for ~$50 to ~$100, and be done with the problem for several years. (now if they were $500 or more, then it would be worth the time fixing.)

No reason at all you can't go a size larger - as long as the mounting is the same, the speed and rotation is right, and it's meant for the duty - usually condenser fan motors are special because they are exposed to the elements, you can't just throw any old motor in there and expect it to live for very long...

Many are special purpose motors, often TEAO (Totally Enclosed Air Over), others are ventilated top or bottom only and/or have special rain slinger rings (shaft up applications) and rain baffles to keep the rain water out. Always put these accessories back on, or get new ones if they break - they are important.

Clean it up (to be nice) and Plop it on the counter at a refrigeration supply house (and write down the make and model number of the condensing unit) and your troubles will soon be over. ;-) They'll have any mounting adapter kits or odd stuff needed, too.

When you are all done, stick an Amprobe on the motor and make sure it's not drawing over the nameplate amps while running - if the airflow through the coils is restricted, or someone else replaced the propeller and put too big a pitch on it :-0 , you can burn out the new motor.

If the coils are full of bugs and crud, pick up a bottle of coil cleaner at the refrigeration house while you're there, and follow the label directions. (Spray on, let sit, hose off. Careful with eyes.) If there are very many fins bent get a fin comb, take off the outer grille and clean it up, makes a world of difference.

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Reply to
Bruce L. Bergman

Yes. Replace it.

Don't do that!

You must match:

voltage HP frame shaft length/dia RPMs thermal-protection run capacitor if you want to reuse the old one (not recommended)

Get it from

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or a local HVAC supply.

You can't change ANYTHING on those motor specs because it's critically matched to the fan blade aerodynamics, condenser resistance, etc. Put in something bigger/smaller/faster/slower and you'll have problems, like the motor overheating.

Fussing with the old bearings never works for very long or reliably, if it works at all.

Remember, every time the condenser fan stalls, your far more costly multi-HP compressor system in insulted with a thermal overload until the thermal shutdown kicks in (you hope it kicks in). Don't mess with the $75 condenser fan!

Reply to
Richard J Kinch

Long range diagnosis is pretty iffy but it could be shorted turns. Either way it sounds as if your motor is due for retirement.

The increase in current for a 1/2 HP motor is unlikely to be a problem but any significant difference in rated full load speed could well rule it out. Fan horsepower varies as the cube of the speed so a speed increase of only

15% would more than absorb the extra HP and overload the motor.

Jim

Reply to
pentagrid

I'm finally getting back to you guys who gave me advice on the fan motor.

Since I had nothing to lose, I took the motor apart one more time and looked inside. Nothing smelled burnt. The rotor turned freely by hand. ... and as I looked at the rotor I noted that it had rubbed at the end where the bearing retainer had come loose. As I looked around some more a glint of something on the stator caught my eye - there were some metal particles sticking to the stator. I wiped them off and cleaned out the case quickly with a paper towel. When I reassembled it, it worked. I suspect that those metal granules were bridging the gap between the rotor and stator at least partially and keeping it from turning.

Thanks again for your advice.

RWL - a fellow self-reliant tinkerer

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Reply to
RWL

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