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  1. #1
    Join Date
    Nov 2003
    Location
    Wisconsin
    Posts
    458

    Condensor fan size/pitch question

    Hey Guys and Gals. Working on an old (35) AAON commercial unit. Condenser fan motor .75 hp as per data plate cuts out on thermal after about 45 min.
    Assume bad bearings even though amp draw not changing, install new with cap. Same pattern. Motor draws 5 amps under load which is under plate specs.I'm thinking someone be fore replaced propeller with wrong one and not enough air moving over motor to cool it. Head pressures do seem to be slightly high. Wondering if using 4 blade fan vs. 3 blade and pitch difference, etc. I'm thinking I'd like to increase air flow by 50% or so. Am on the right track?
    Thx
    Rango
    In my many years I have come to a conclusion that one useless man is a shame, two is a law firm, and three or more is a congress. John Adams

    The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. H. L. Mencken

    "Life's tough......It's even tougher if you're stupid."
    -John Wayne

  2. #2
    Join Date
    Sep 2004
    Location
    Phoenix, Arizona
    Posts
    88
    Ummmm... no...lol.. what is the name plate FLA? If your close to being under then fan blade is correct. If there is not enough load a motor will over heat. Check voltage, connections, make sure the blade is in the center of the openning.

  3. #3
    Join Date
    Nov 2003
    Location
    Wisconsin
    Posts
    458
    Amp draw is just under plate value.
    seems like more air is necessary for cooling.
    In my many years I have come to a conclusion that one useless man is a shame, two is a law firm, and three or more is a congress. John Adams

    The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. H. L. Mencken

    "Life's tough......It's even tougher if you're stupid."
    -John Wayne

  4. #4
    Join Date
    Dec 2000
    Location
    Flat Rock, NC
    Posts
    463
    original motor spec may have been for 60C motor for condenser applications. Verify clean coil. some 3/4 motors have lower amp rating than others. also is rpm correct?

  5. #5
    Join Date
    Nov 2003
    Location
    Wisconsin
    Posts
    458
    Coil clean,rpm correct. Label says original motor was 6.75 amp.
    In my many years I have come to a conclusion that one useless man is a shame, two is a law firm, and three or more is a congress. John Adams

    The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. H. L. Mencken

    "Life's tough......It's even tougher if you're stupid."
    -John Wayne

  6. #6
    Join Date
    Dec 2000
    Location
    Flat Rock, NC
    Posts
    463
    Sounds like you need a higher amp rated motor, sometimes you go with a higher hp to match amp draw of spec. motor.

  7. #7
    Join Date
    Apr 2009
    Location
    massachusetts
    Posts
    67
    Don't know why but when a condencer fan motor goes on a aaon your better off getting repl. directly from aaon. Had a summer when I tried everything then someone from talk straightened me out,almost a proprietary thing.

  8. #8
    Join Date
    Nov 2003
    Location
    Wisconsin
    Posts
    458
    Since Larry retired, nobody at AAON knows anything about these old units unless you have the part number,and then it's just the part.
    In my many years I have come to a conclusion that one useless man is a shame, two is a law firm, and three or more is a congress. John Adams

    The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. H. L. Mencken

    "Life's tough......It's even tougher if you're stupid."
    -John Wayne

  9. #9
    Join Date
    Jul 2013
    Posts
    63
    Does the motor say to use ex: 5 cap with 240 volts and at 7.5 at 208?

  10. #10
    Join Date
    Nov 2003
    Location
    Wisconsin
    Posts
    458
    Nope, 10 mf
    Cap circuit only running .70 amp
    In my many years I have come to a conclusion that one useless man is a shame, two is a law firm, and three or more is a congress. John Adams

    The whole aim of practical politics is to keep the populace alarmed (and hence clamorous to be led to safety) by menacing it with an endless series of hobgoblins, all of them imaginary. H. L. Mencken

    "Life's tough......It's even tougher if you're stupid."
    -John Wayne

  11. #11
    Join Date
    Jul 2013
    Posts
    63
    Strange. The old motor did the same thing? What's change? How long has the unit worked before hand because if its worked for years then the fan blade isn't the issue. No play in the bearing moving the shaft up and down? Spins free? I've seen motors bad out of the box but doubt it. And it's for sure going out on thermal? I would say check voltage but you've answered that with amp draw.

  12. #12
    Join Date
    Sep 2006
    Location
    Ohio
    Posts
    473
    If the fan blade originally had a three prop blade and now you have a four prop blade, that will make the amp draws go up. The Aaon RTU's I have worked on always have three prop blades.

  13. #13
    Join Date
    Sep 2004
    Location
    Phoenix, Arizona
    Posts
    88
    Sorry I didn't see what the amp rating on your current motor was? I always sized my motors to match ampeage as close as possible to unit name plate amps. OEM does strange designs on their motors to get what they are looking for, indoor blower motors are worse. Replacement motor are generic and the HP doesn't always match the the load it is working at. Also raising and lowering a fan blade inside the fan orfice will change the amount of air it moves, and you can see that in your amperage. Thats a way to fine tune a generic motor. 3, 4 or 5 blades can all work if the blade pitch is less as you go up in number of blades. LAUparts.com has a fan to HP motor chart you can download online. Sometimes I had to up an HP size to make a motor work. In 20 yrs I hardly had a problem here in Phx replacing motor/ fans.

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