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Thread: AO Smith pump motor hums but won't start

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    AO Smith pump motor hums but won't start

    Five year old Century Centurion. The condition results in either tripping the circuit breakers or tripping the internal thermal switch which automatically resets after a cool off period (it makes the click noise). I have verfied that the capacitor is good. I removed the motor shaft end cover to confirm the motor turns freely and is not seized.

    Here's the kicker....this is a repeat problem. The same thing occured last season at this same time of year. Water temp is ~ 45 degrees. Ambient temps are low 30s at night and low 60s during the day. When this occured last season, I decided to leave the system off and deal with repairs when the swim season was closer. When the weather warmed in early spring, the pump started and operated through the warm season with no indication of problems. Now, back in winter, I'm experiencing the same problem. I can only conclude the problem is associated with the cold.

    Has anyone else experienced this? Is there an internal switch or other component that might be sensitive to the cold that I can access to clean or otherwise replace? Also, can the motor be removed from the pump assembly without removiing the entire motor/pump assembly from the pool system?

    Thanks in advance for any help or input.

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    Mod Squad Bama Rambler's Avatar
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    Jun 2009
    SouthWest Alabama

    Re: AO Smith pump motor hums but won't start

    Some motors have a centrifugal switch on the outboard shaft end (away from the pump side) that may be sticking or the contacts may be pitted. It acts the same as having a bad capacitor. Free it up and buff the contacts with sandpaper and see if that fixes your problem.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
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    Re: AO Smith pump motor hums but won't start

    Thanks Dave. I'll investigate this further.

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    Re: AO Smith pump motor hums but won't start

    not associated with cold, its a time thing with smith motors. go switchless and capacitorless

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    Re: AO Smith pump motor hums but won't start

    Thanks...I removed the motor from the pump assembly and it runs just fine immediately coming to speed smoothly and quietly. Upon further inspection, the O ring between the diffuser and volute assembly was stretched out of shape allowing water to enter the areas around the diffuser, impeller, and motor shaft. Corrosion was present in those areas creating additional friction and drag on the motor preventing it from starting. About $125 to replace those parts.

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