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Thread: hum from outdoor heat pump

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  1. #1
    DIY Member GregO's Avatar
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    Default hum from outdoor heat pump

    Hi,

    I've got a Trane XL13i - outdoor unit has a low electrical hum, even when the power is off, meaning even after tripping the electric breakers for the indoor furnace and the outdoor unit. The hum best mimics that of a fluorescent light tube hum; it's not real loud and the unit seems to work (cycle) perfectly fine, although the capacitor has been replaced twice and the unit is 10 years old.

    Any idea what is causing this hum? Thanks!
    Greg

  2. #2
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by GregO View Post
    Hi,

    I've got a Trane XL13i - outdoor unit has a low electrical hum, even when the power is off, meaning even after tripping the electric breakers for the indoor furnace and the outdoor unit. The hum best mimics that of a fluorescent light tube hum; it's not real loud and the unit seems to work (cycle) perfectly fine, although the capacitor has been replaced twice and the unit is 10 years old.

    Any idea what is causing this hum? Thanks!
    Greg

    It may be the 24 Volt transformer that is on another breaker.

    Is it popping your breaker ?

    What is your complete model number ?

    What is the value of the cap you are replacing ?


    Good Luck.
    Last edited by DonL; 09-24-2013 at 04:44 PM.
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  3. #3
    DIY Junior Member kyleanderson's Avatar
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    Hello
    There is power to indoor unit send low voltage to contractor. Maybe you are missing an breaker. There could be two branch circuits to indoor unit one being 60 amp and another being 30 making indoor unit 15KW backup heat kit installed. What you are have is contractor calling for heat or cool. On the outside unit take the yellow low voltage wires and disconnect them and buzz should stop.

  4. #4
    DIY Member GregO's Avatar
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    There's a 40-amp double breaker for the indoor furnace and a double-60 amp breaker for the outer unit...I think...I say that because that's all the breakers obvious/labeled for the HVAC. The system seems to work fine otherwise, but I don't recall hearing that humming sound ever when the HVAC system wasn't running at all.

    Greg

  5. #5
    Jack of all trades DonL's Avatar
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    Your 24 Volt transformer that the thermostat uses may be on a different breaker and will normally be feed by 120V. Some are shared with the Doorbell.

    When the gas in the unit is equalizing it will make noise, but not really a hum.

    Can you post audio ? Is it 60 Cycles ?

    The crankcase heater may hum a bit, but power would need to be applied.


    Good Luck.
    Last edited by DonL; 09-25-2013 at 12:02 PM.
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  6. #6
    Electrical Contractor Bobelectric's Avatar
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    Those days of a shared xfmr are long gone. Never saw a 24 volt doorbell.

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Bobelectric View Post
    Those days of a shared xfmr are long gone. Never saw a 24 volt doorbell.

    I think sharing is a common practice. May not be the same transformer, but the same circuit.

    I have seen transformers located in the Convenience outlet for a furnace or air handler.

    24V is a standard MAX voltage. Most Doorbell chimes will have a on board regulator. As do the electronic controls in the newer HVAC systems.

    It may share the Alarm / Fire system , and is on a always on circuit, Nice ones have battery backup, and the transformer charges the backup batteries.


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