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  1. #1
    Join Date
    Apr 2003
    Posts
    33

    Question Fans Running Slow

    Hello to all I have a 30 ton RTU Lennox unit thats about 9 years old. Its been a good unit till now. I got a call for a lack of cooling from the unit,what I found was that it was tripped out on High Pressure, the whole unit!!. After I reset it.
    I found 1 fan locked up 1 not running and the other 4 running about half the speed they normally due (these are single speed fans) they are 480VAC single phase 1/3 hp motors. I could not dive into it because of a heavy rainstrom thats still dumping and its been 4 hrs and its not letting up. I would appreciated any words of wisdom on the matter(this is something that I have never seen before). Thanks Addison Ft Worth Texas

  2. #2
    Join Date
    Dec 2001
    Location
    Southern Tier, NY
    Posts
    6,066
    Hmmmmnnn ....

    fix the C.F. Motors ...????

  3. #3
    Join Date
    Jun 2005
    Location
    Sparta, Tenn.
    Posts
    40

    Fuses

    Check you fan fuses, one is blown. Causing 480 volt fans to run slow

  4. #4
    No such thing as 480 volt single phase.... 480 to neutral is 277 VAC which is single phase................ slow turning motors?........ start at the capacitor... a PSC with a bad...er open cap will run only on the run winding..... a motor running in a single winding is called a split phase.... which my guess is not what you have for fan motors............

  5. #5
    Join Date
    Oct 2006
    Location
    Central Texas
    Posts
    649
    Check your connections & capacitors ( are you using two seperate caps. or one?) Is the motor which is turning slowly does the speed ever pick up? If it does p/u sounds like motor bearings. Can you touch touch the motor?... is it hot?. Amp draw, what's it rated for Vs. actual amps? Hope this can help.
    Sic Semper Tyrannis.

  6. #6
    Join Date
    Dec 2003
    Location
    Location!, Location!
    Posts
    929
    480 volt, 2 wire(phases), a+b or a+c or b+c = 480. 1 phase angle.
    but it sounds like a blown leg(fuse), and backfeed through a load, what's the voltage at the slow fans- that will tell you. Also are all 4 fans drawing off the same 2 legs or are they balanced between the 3? check fuses first.

  7. #7
    Join Date
    Aug 2006
    Posts
    442
    Quote Originally Posted by coronado2412 View Post
    No such thing as 480 volt single phase.... 480 to neutral is 277 VAC which is single phase................ slow turning motors?........ start at the capacitor... a PSC with a bad...er open cap will run only on the run winding..... a motor running in a single winding is called a split phase.... which my guess is not what you have for fan motors............
    What do you mean no 460 single phase??????

  8. #8
    Join Date
    Mar 2007
    Location
    San Diego CA.
    Posts
    16

    Addison Junk

    You will read 240V on each leg to make single phase 460. Check and see if it has either a small vfd or the motor runs on a pressure switch to controll speed.I have a addison which I maintain and it has the same set up.
    Last edited by Coremech; 03-26-2007 at 11:48 PM.

  9. #9
    Join Date
    Aug 2006
    Posts
    442
    277 between hot leg and ground.

  10. #10
    Join Date
    Aug 2006
    Posts
    442
    460 between two hot legs

  11. #11
    Join Date
    Mar 2007
    Location
    San Diego CA.
    Posts
    16
    460 on two legs 240 to ground. On my paticular unit it has a johnson controll vfd which controls the motor speed. I also had a old trane condensor with the same set up as well except for the drive.

  12. #12
    480 on 2 legs, 277 on either leg to ground.

  13. #13
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by Coremech View Post
    You will read 240V on each leg to make single phase 460.

    WRONG you wil read 277 on each leg to ground, 2 legs of 277 equals 460 volts, its usually actual 480 volts!

    and i never seen a hot leg with a 460 volt circuit!



    .

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