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My AC unit fan stopped working suddenly. I tested the 3 pole condenser (capacitor) and the it looks OK ( 45 uf , 5 uf is what is mentioned in the spec of capacitor). I tested the resistance in the the wires going to the fan motor and it turn out to be 30 Ohm 50 Ohm and 80 Ohm. so there is no open in the motor. Does it mean Motor is fine?

contractor should be OK (** and i am assuming it **) as it is powering the compressor correctly. What can be the way to debug it further.

I can say with reasonable confidence the compressor is OK as i am still getting the cold air at vent also compressor temperature is rising up when the unit is ON.

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    Check for bad/damaged/loose wiring between the contactor and the capacitors, and the capacitors and the motor. Can you rotate the fan by hand? Does the motor produce any noise, vibration, or heat when the unit is on? Is there any debris preventing the fan from spinning?
    – Tester101
    Commented Aug 12, 2014 at 12:54
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    At the risk of sounding blatantly obvious, the motor shaft could be frozen. This happened to me and it was obvious when I could not easily turn the fan by hand. Assuming you've already done this then I guess we'll have to wait for a more experienced person to chime in.
    – glw
    Commented Aug 12, 2014 at 15:32
  • @Tester101 thanks! I checked the connection and everything looks ok to me as far as connections are concern. I can rotate the fan blade by inserting a stick inside the Louvered steel top. its hard to tell about the noise coming from motor as compressor noise masks it. is there any way i can turn off the compressor selectively. Also is it possible that contactor is good for compressor but bad for fan?
    – David
    Commented Aug 12, 2014 at 18:45
  • @glw3 thanks. Yes the fan motor is not Jam. I can rotate the blade, but it does have some friction.
    – David
    Commented Aug 12, 2014 at 18:46
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    @David You can certainly disconnect the compressor, and run the unit with only the fan. However, if you don't know how to do so, I'd say you're in over your head and should contact a professional.
    – Tester101
    Commented Aug 12, 2014 at 21:14

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The problem was because the RPM of the new motor was different. So it burned out quickly. Make sure to use the same RPM motor apart from the HP and Amp of the motor. It really makes the difference. the AC guy now installed the same RPM motor and it works great.

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