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Old 06-22-2010, 04:28 PM   #1
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New fan motor going out?

I had a local technician come out last week and check my unit, (it was blowing ambient air, not cooling), but it worked perfectly the entire time he was there, so he deduced by the symptoms that the condenser fan motor was overheating and shutting down.

His quote of over $1000, ($730 for fan motor, two capacitors 1@$187 and 1@$137) seemed a bit steep to me, so I was going to replace the motor and capacitor myself.

Turns out, our daughters brother in law is in the business so he came over and replaced the motor and installed a new capacitor.

That was last Tuesday, it ran perfect all week, but then yesterday the fan started shutting down again. And it was extremely hot to the touch. Same symptoms as before, during the heat of the day it would run for an hour or so and then shut down and blow ambient air.

Since I was going to do it myself I had researched the motor and capacitor etc. So when he replaced it I made sure he used a motor with similar specs.

1/3 HP, 1075 RPM, 208-230V, Phase 1, 60Hz, 48Y frame, etc. I did not confirm the capacitor specs, which I will now do. He used an A.O Smith motor. This is a Comfortmaker all in one roof top unit.

The only differences in what he did vs. the old motor:

1. The motor he used had a inch shaft when the original was 5/8, so he used a sleeve on the shaft to compensate.
2. He situated the fan a little higher (closer to the motor) than the original.
3. He wired in a new separate capacitor, the original was sharing a dual can capacitor with the compressor.

It is blowing the correct direction, up and out pulling air through the coils.

There were 4 screws in the sides of the motor that I noticed seemed like they had backed out, I tightened them up yesterday, not that I expected that to be the problem, it did not help.

From what I have written can anyone tell me what might be going on?

Did he possibly wire it incorrectly? (it worked great for a week?)
Could it just have been a bad motor?
Perhaps the incorrect capacitor for the motor?
Even though it is a roof top unit and there is no debris against the coils, could they be dirty and need cleaning?
Will I need a new motor altogether, even if this one overheating and shutting down is it maybe still ok, if I can solve the root problem? (Heck it is brand new)

I am going to check it with my volt meter this afternoon when I get home to see what is going on as far as electricity flow.

Any help is greatly appreciated.


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Old 06-22-2010, 04:45 PM   #2
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could be a number of things. not sure you should have used a separate capacitor, i would have stuck with a dual run capacitor matched for the new fan motor. you need to know what the specs were on the old, OEM motor and compare the differences. you don't have all the specs listed. are they the same FLA (full load amperage)? in other words, do they match EXACTLY, because if they don't, a different capacitor with the proper rating is most likely needed. i think there is also the slight possibility that rasing the blade higher on the shaft could potentially cause a problem, but i'd say this is less likely to be the issue. i'd at least situate the fan blade the way it was before just to be sure.

best guess is that your new motor is over-amping. look at the FLA on the motor and measure the actual load to the motor when it's running. usually the condenser will have the FLA and HP of the OEM fan on a spec tag somewhere.


Last edited by NitroNate; 06-22-2010 at 05:00 PM.
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Old 06-22-2010, 05:14 PM   #3
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Thank you NitroNate,

I know that the motor that was replaced last week was rated at 1.7 FLA, I am not positive of this new one but will definitely be verifying it along with the new capacitor today. I had seriously thought about lowering the fan about an inch and half to where is was situated before as well. I might just give that a shot, see if it makes a difference.
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Old 06-22-2010, 06:07 PM   #4
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The fan blades being higher, is not good.

As said above. Is the new motor rated at the same amperage.

Yes, a dirty coil can cause this.
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Old 06-22-2010, 08:09 PM   #5
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Was the blade changed with the motor? You mentioned the shaft sizes were different. Maybe a new blade with the wrong pitch was installed and is overloading the motor. Capacitor could also be miswired.
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Old 06-23-2010, 10:38 AM   #6
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Thank you everybody for your input.

Funny thing, with the new motor the whole system sounded different, hard to explain but it had this whole different sound, last night I lowered the fan about an inch, and what do you know the sound was back to normal, and it worked the whole evening, did not shut down once. I am going to keep my fingers crossed.

The previous motor was rated at 1.7 AMPS and the new motor is rated at 1.8 amps, I verified that it has the correct capacitor, right on the motor it calls for a 7.5UF cap, and that is what is currently installed.

The fan was not changed, a sleeve was used to re-size for the smaller shaft.

I think the next step will definitely be cleaning the coils. But so far so good.


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