outside ac unit fan won't run

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Old 09-22-09, 04:59 PM
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outside ac unit fan won't run

My Bryant ac unit fan motor on the top of the condensor unit won't run. The fan inside the furnace unit runs, but does not blow cool air.
The fan motor outside gets really hot, but does not run. I actually got it to run by spinning the fan blades with a stick. It ran for about five minutes then cut out again. I can hear the unit engage when I throw the breaker outside, but the fan won't run.
Do I need a new fan?
 

Last edited by namort; 09-22-09 at 05:08 PM. Reason: spelling
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Old 09-22-09, 05:16 PM
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Either a new capacitor or motor. If capactior looks obvious bad with a bulge in it's can or some discoloration or some ooze coming from it, it is bad for sure. But if nothing apparently wrong, it still may be weak. They cost maybe $10. Not a bad gamble. Or just take it all to the motor shop.

Oddly, before I came online tonight, I'm up on a rooftop commercial unit and the fan is 'locking' when energized to run, and spins fairly okay when not energized. Ohms test says motor is good. Motor shop guy said bearing may be bad anyway. And yes I can hear growling when I turn it, yet there is no side to side play. On this ball bearing motor he should be able to redo them at my discretion at 1/3 cost of a new motor. Tomorrow he is to check it out. But in your case, you'd need another motor. Go thru a motor shop as they should be cheaper there than furnace supplier.
 
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Old 09-22-09, 08:45 PM
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I'd replace the fan motor and the capacitor.
Sounds like the capacitor went bad first.
But the motor has been getting hot because it can't start.
Almost 100% chance it has been overheated, the lacquer on the windings has been cooked and the heat has burned the oil that was on the bearings.

I'd just replace them both or you will most likely SOON be back to replace whichever one you don't replace now.
 
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Old 09-22-09, 09:20 PM
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Thanks for the info. It sounds like home depot is not the place to get these parts; what type of place has these? Also, to find out if the motor should be rebuilt or replaced, do I just take it to an ac motor shop?

Also, what is the best way to discharge the capacitor when I replace it?

Thanks again
 

Last edited by namort; 09-22-09 at 09:23 PM. Reason: additional question
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Old 09-23-09, 07:16 AM
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You may or may not have a charge in the capacitor. There are methods about how to properly discharge one on the internet. Some people (even on this forum) simply say to bridge the opposite tangs of the capacitor with a screwdriver. Other info I have read says to install about a 2 or 3 watt bulb between a set of wires before grounding out. If shorting with a screwdriver is the way to go, then why would seemingly professional advice say to use a form of a resistor? So I believe in always erring on the side of caution.

I simply use my voltmeter, itself as the resistor, set to 750 volts (especially on 480 equipment), and do everything imaginable with that voltmeter to be certain no volts are in it. I will set to ac volts and put probes on the opposite spades. Then I will even reverse the probes to be sure. (albeit probably unnecessary when ac and not dc) Then I will put the red probe on one spade and put the black probe to sheetmetal. And do the same to the other opposing spade. If everything comes up 0, it have no charge in it.

Recently I was working on 480 volt system and almost everytime I'd remove wires from any capacitor, even after the equipment just ran, my tests on all 4 capacitors would show 0, or a low number that quickly became 0. And even at that, before removing the wires, out of skeptism I'd quickly one-handed, 2-fingered touch the 2 spades, after it sadi 0. Everytime, I'd have no residual voltage in any of the capacitors on the big handler units.

Well, one day when one of the motors went down, I did that same voltmeter test described about, and the voltage started out like 550!!! on my meter, when one multimeter probe was on one spade and the other probe was on the other spade. And as I held it there, it bled down, slowly. The volts kept dropping and dropping until it went to 0. My meter is acting like a resistor in it's own right, like the 2 watt bulb idea. Sure glad I did not handle that capacitor based on how 90% of the time very little charge has been found in the capacitors!!! [And a word of advice when even using a voltmeter, and your life might depend on what it says: You then need to verify afterwards that the meter still works!...that it did not short out or something during the testing/discharge(same could be said if no light showed anymore through the 2 watt test bulb), and you are falsely being decieved!

And yes, just go to some motor shop. That is where I have to go shortly. I have to verify if the bad bearings is really the sole cause of electrical motor lock occuring, because my motor ohm readings are all coming up good, compared to all 15 other motors we have that give the same reading.
 
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Old 09-23-09, 05:32 PM
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Update

Originally Posted by ecman51` View Post
And yes, just go to some motor shop. That is where I have to go shortly. I have to verify if the bad bearings is really the sole cause of electrical motor lock occuring, because my motor ohm readings are all coming up good, compared to all 15 other motors we have that give the same reading.
To any of the curious - the prognosis was that the spring loaded thrust bearing was allowing more than normal end play which finally caused the rotor laminates to dig in and stop the motor, only when energized, and the rotor was pulled down electrically. (The motor is shot and needs to be replaced, he said. Not worth trying to rebuild.).

That explains why I could spin the motor by hand, when not energized, and why all the motor leads ohmed out properly, and no short. Interesting. Something else for me to file away in my cluttered mind.
 
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