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  1. #1
    Join Date
    Feb 2008
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    California
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    2,057

    Why do package A/C units have 3 phase compressors and single phase blower/condenser?

    Why do package A/C units have 3 phase compressors and single phase blower/condenser fan motors?

  2. #2
    Join Date
    Sep 2007
    Location
    NH
    Posts
    1,110
    Cheaper to build em that way would be my guess on the smaller ones... But most 20 ton and up units have 3 phase condenser fans and evap motors.. Heck even most package units 5 ton and up have 3 phase evap motors.

  3. #3
    Join Date
    Feb 2009
    Location
    Winnipeg MB
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    13
    Quote Originally Posted by Dchappa21 View Post
    Cheaper to build em that way would be my guess on the smaller ones... But most 20 ton and up units have 3 phase condenser fans and evap motors.. Heck even most package units 5 ton and up have 3 phase evap motors.
    agreed.

  4. #4
    Join Date
    Aug 2011
    Location
    Salem Oregon
    Posts
    26
    I suspect has to do with economy of scale. A factory can produce a million 3/4 horse single phase motors more cheaply per motor than the factory that produces a quarter million3/4 horse three phase motors. So when Trane or Carrier needs a blower motor at a certain hp, the single phase wins sometimes.

  5. #5
    Join Date
    Aug 2006
    Location
    Mixing oil and fire with a big spoon.
    Posts
    4,008
    yep....costs.

    a 1 hp, 1800 rpm, 1 phase condenser fan motor has an amp draw of 3.2 amps at 460 vac.
    a 1 hp, 1800 rpm, 3 phase condenser fan motor has an amp draw of 1.5 amps at 460 vac.

    this isn't much of an efficiency drop but it is a huge drop in costs...small relays instead of contactors, less weight (remember shipping costs money from the manufacturer of the motor to the unit manufacturer and from them to the end user...it gets shipped twice), lighter duty mounting brackets (3 phase motors are a bit torquier than their single phase brothers), etc.

    i used a 1 hp motor because it was all i could find data on in both a single phase and a three phase.
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  6. #6
    Join Date
    Sep 2005
    Location
    Atlanta GA area
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    20,259
    Probably cost.

    Used to do RTU's do not do them anymore (tired of climbing ladders). Seems Voyagers from around 10T and up, especially 460V, had 3 ph motors... smaller ones did not.

    I wonder how long until we see ECM style (X-13) motors start to take over?
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  7. #7
    Join Date
    Dec 2012
    Location
    Illinois
    Posts
    147
    I've got a location with some 2 year old 208v trane units that are 5 ton each that use 3 phase cond fan motors with heat sinks clamped around them. They are also direct drive indoor blowers. I think they are 3 phase on ac drives. That could be wrong, but they do have variable speed controls.

    I'm right with ya, it's always bugged me, when they have the ability to use a more efficient 3 phase motor why they would put more parts in to fail.

  8. #8
    Join Date
    Aug 2006
    Posts
    2,552
    Quote Originally Posted by CFESAmasterEGSR View Post
    I'm right with ya, it's always bugged me, when they have the ability to use a more efficient 3 phase motor why they would put more parts in to fail.
    You hit the nail on the head. Most of you never heard of a Worthington Unit, it was extremly rare to ever have to replace anything other than filters and belts. I think they put themselves out of business, because they didn't have the replacement parts income.

  9. #9
    Join Date
    Oct 2012
    Location
    Wisconsin
    Posts
    2,664
    On some of the Lennox 5ton rooftops they have a two-speed direct drive indoor blower that is single phase, lower speed for heat, high speed for cool (I could be mistaken, don't run into the little rooftops that much). All the larger units are belt drive and have three-phase blowers. The condenser fans are single phase, they are 1/3hp.

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