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  1. #1
    Join Date
    Aug 2008
    Posts
    5

    AC Motor Overheating Question

    Hello All,

    I am not an HVAC person, but I am an engineer and I was hoping some of you could give me some information. I live in an apartment with a large central AC unit, and in each apartment there is simply a blower unit that pulls cold form the central circulating system.

    The motor on this blower unit keeps overheating and shutting down. (Way to hot to touch). The apartment fix it guy says it has been replaced, and is installed correctly, and that we are simply "Overworking" the unit. The apartment never gets cool in that it is always in the mid to low 70's. He think that this is acceptable, and that setting the unit on 68 is what is causing the problem.

    I would think a motor in a unit like this should be able to run almost continuously without overheating like this. As it is it can't run for more then 15 to 30 minutes without overheating. I would also think it is not unreasonable to want my apartment at 68.

    Can you experts give me any feedback or ammunition I can use with this guy who clearly does not want to fix my problem.

    Any help is really appreciated!!

    Thanks
    James

  2. #2
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    The guy is right. (to a point. But I can't eleborate because of the forum rule of no DIY)

    But make sure your filiters and evap are clean.

  3. #3
    Join Date
    Aug 2008
    Posts
    5
    I don't want any DIY information. The forum rules only say no step by step instructions, and that is great I have no interest in fixing this myself. All I want to know is, if I am being snowed by the maintenance guy. Really, answers to these questions:

    1. How long should a motor in a unit like this be able to run? 30 minutes? An hour? 5 minutes? 6 hours?

    2. Should a brand new building, with brand new cooling units be able to be Air conditioned to 68 degrees? Or is my apartment never going to be below 75 and is that a reasonable expectation?

  4. #4
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Shuold an a/c be able to run at 68*? A lot of people would argue against it.

    I run mine at 66, but I have made modifiacations to protectct the system from damage.

    I don't know how your system was designed. But I would have to say the blower going down on O/L is not normal.

    Are the filters clean?

    Has the unit ever been able to pull down to 68* in the past?

  5. #5
    Join Date
    Apr 2007
    Posts
    6,285
    How hot is it outside?

    If the units are brand new check your filter.

    The motor should be able to run constantly unless there is something wrong with the duct work. Do you have vents closed off? Are all the doors in the apt. open? Are the blinds shut to keep radiant heat out? Are bath vents off and dryers not running during the hot part of the day? If you have a fire places is the flue shut? Is anything blocking the return vent?

  6. #6
    Join Date
    Aug 2008
    Posts
    5
    I am in Denver CO, and it has been very cool lately for August. In the 80's mostly, with a few low 90's.

    The building is literally brand new (15 stories), and the unit is new.

    The maintenance guy has removed the filter completely.

    None of the vents even close, and literally I think the longest duct can't be moire then 5 feet, yet I feet hardly any air when I hold my hand up to one of the vents, even with the blower on high.

  7. #7
    Join Date
    Aug 2008
    Posts
    5
    Oh, no dryer, fireplace at all. No bath vents running. Blinds closed all day when I am not there. Also, the apartment is only 700sqft, and I leave all doors open to circulate the air.

  8. #8
    Join Date
    Aug 2003
    Location
    Lincoln, Nebraska
    Posts
    1,051
    68° is mighty cold to keep an apartment. Most systems in our area are designed so that on a 95° day it will maintain 75°. That being said the motor should be able to run constantly and not go off on the overload as it seems to be.

    One other thought is maby there is some sort of saftey that is shutting off the unit at a certain temperature that the apartment owners want it to be. Hard to tell from here. Who pays for the utilities?
    Its a good Life!

  9. #9
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    HMMMMMM///


    Time to have a pro come look at the cooling coil.

    I'm thinking the coil is plugged with construction debris.

    Why in god's name did you not insist the on a new filter from maintenance?

    I am sorry to say if you have been running this a/c with out the filter you are culpable.

    You stated you are an engineer sir, you should know better than to run a mechanical device you knew needs a filter. But it's too late for the filter now anyway.

    Call a company to examine the cooling coil. I think yo will find it so restricted with dry wall dust that the air has no place to go and it is over loading the motor.
    Last edited by hvaclover; 08-12-2008 at 04:12 PM.

  10. #10
    Join Date
    Jun 2006
    Posts
    294
    Regardless of the A/C usage the blower should be rated for continuous service and the Tech is absolutely wrong in his explanation, The filters have nothing to do with the problem as anybody in the business should know that a dirty filter , in fact puts LESS load on the blower, not more. Moreover, as I understand it you are blowing into an "open" area, so, that is the basic design with no ducting. If not, then oversized ducting could cause the problem but small ducting would not.

    One key to whether the guy is snowing you is if the previous motor worked without this problem. In any event HE should be solving the problem and not giving you EXCUSES, especially those.

    This may be an incorrect replacement motor, or a wrong or leaking running capacitor , or the motor is overloaded for other reasons like incorrect voltage or bad bearings. A final possibilty is lack of convection cooling over the motor shell.

  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,011
    Quote Originally Posted by sskzekeman View Post
    Regardless of the A/C usage the blower should be rated for continuous service and the Tech is absolutely wrong in his explanation.

    I totally agree! and the motor might be running backwards if he feels hardly any air at all.
    __________________________________________________ _______________________
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  12. #12
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by sskzekeman View Post
    Regardless of the A/C usage the blower should be rated for continuous service and the Tech is absolutely wrong in his explanation, The filters have nothing to do with the problem as anybody in the business should know that a dirty filter , in fact puts LESS load on the blower, not more. Moreover, as I understand it you are blowing into an "open" area, so, that is the basic design with no ducting. If not, then oversized ducting could cause the problem but small ducting would not.

    One key to whether the guy is snowing you is if the previous motor worked without this problem. In any event HE should be solving the problem and not giving you EXCUSES, especially those.

    This may be an incorrect replacement motor, or a wrong or leaking running capacitor , or the motor is overloaded for other reasons like incorrect voltage or bad bearings. A final possibilty is lack of convection cooling over the motor shell.
    You'Re saying a dirty filter won't cause a motor o/l to trip open?

    I think you should explain that one.

  13. #13
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by sskzekeman View Post
    Regardless of the A/C usage the blower should be rated for continuous service and the Tech is absolutely wrong in his explanation, The filters have nothing to do with the problem as anybody in the business should know that a dirty filter , in fact puts LESS load on the blower, not more. Moreover, as I understand it you are blowing into an "open" area, so, that is the basic design with no ducting. If not, then oversized ducting could cause the problem but small ducting would not.

    One key to whether the guy is snowing you is if the previous motor worked without this problem. In any event HE should be solving the problem and not giving you EXCUSES, especially those.

    This may be an incorrect replacement motor, or a wrong or leaking running capacitor , or the motor is overloaded for other reasons like incorrect voltage or bad bearings. A final possibilty is lack of convection cooling over the motor shell.
    You'Re saying a dirty filter won't cause a motor o/l to trip open?

    I think you should explain that one.
    Last edited by hvaclover; 08-12-2008 at 03:43 PM.

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