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  1. #1
    Join Date
    Jun 2011
    Location
    Fredneck MD
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    12

    scrolls running backwards

    Ok heres one that will stump you. Well it stummped me and my HVAC buddies anyways.

    The lobby unit in our building has been running 24/7 for 3 years with no problems. Then one day out of no where we found the main breaker for the unit tripped. After a quick investigation we reset the breaker and the compressors sounded horrible. we assumed a mechanical failure, but threw guages on it anyways and found the pressures to be equal while the compressor was "running".

    So heres where it gets interesting. The fan is rotating properly, however my boss decided to switch 2 of the 3 legs on the compressor to change its direction and what do you know, the compressor ran perfect!

    Hopefully i gave you guys enough info. So what do you think, were stumped?

  2. #2
    Join Date
    Jul 2010
    Location
    So-Cal
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    585
    Disgruntled employee?

    Sabatoge?


  3. #3
    Join Date
    Jun 2011
    Location
    Fredneck MD
    Posts
    12
    Quote Originally Posted by jackintheboxtec View Post
    Disgruntled employee?

    Sabatoge?

    That crossed our mind, but if it was we cant pin point it

  4. #4
    Join Date
    Jun 2011
    Location
    Houston area
    Posts
    1,493
    A scroll with a switched leg and running backwards WILL sound like a train wreck and won't develop a pressure diferential. The fan(s) are probably single phase motors and don't give a hoot.

    If it ran for three years and suddenly something like that happened then somebody or something did a change up.

    Have there been any recent Bigfoot sightings in your area lately? Those hairy sob's have known to fish without a license.
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

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  5. #5
    Join Date
    Jun 2011
    Location
    Fredneck MD
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    12
    Quote Originally Posted by Cooked View Post
    A scroll with a switched leg and running backwards WILL sound like a train wreck and won't develop a pressure diferential. The fan(s) are probably single phase motors and don't give a hoot.

    If it ran for three years and suddenly something like that happened then somebody or something did a change up.

    Have there been any recent Bigfoot sightings in your area lately? Those hairy sob's have known to fish without a license.
    The fans are actually 3 phase too, and running normally.

    I guess i need to start thinking of all of the people i've pissed off lately

  6. #6
    Join Date
    Sep 2011
    Location
    Alabama
    Posts
    3
    I have seen it years ago when the power company replaced a blown pole mounted transformer. They paced the 3-phase wire back differently. The phase shift on the wire change made it run backwards. It is not uncommen. Sometimes when the power goes out it happens.

  7. #7
    Join Date
    Apr 2005
    Location
    where the beer flows like wine
    Posts
    2,871
    I encountered the very same problem with a two stages Carrier RTU, one of the compressors ran backwards for five years or so, nobody notice it, I also thought the compressor was shot but after swapping leads it ran like a champ, amazing it survive after running backwards for so long.

  8. #8
    Join Date
    Dec 2007
    Location
    houston, texas
    Posts
    3,787
    Had a Trane unit do the same thing, one day the compressor was running backwards for no apparent reason, switched the leads and away it went.

    Had the same thing with a 3 phase 7.5 hp blower motor.
    I'm not tolerating Political Correctness anymore, from now on it's tell it like it is.

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  9. #9
    Join Date
    Oct 2002
    Posts
    1,394
    Back to back three phase motors running on single phase (bad contactor or breaker causing missing leg) will recreate the missing leg. Three phase motor would work on a single phase supply then

    This is how one can use a three phase motor on single phase service.

    Maybe?

  10. #10
    Join Date
    Apr 2005
    Location
    where the beer flows like wine
    Posts
    2,871
    Quote Originally Posted by timjimbob View Post
    Back to back three phase motors running on single phase (bad contactor or breaker causing missing leg) will recreate the missing leg. Three phase motor would work on a single phase supply then

    This is how one can use a three phase motor on single phase service.

    Maybe?
    I've seeing 3 phase motors running on 2 legs but as soon as the motor stops it wont start back up again,it hums,get hot trip or burn.

  11. #11
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
    Posts
    1,874
    The OP didn't state if it is 3 or single phase. Older single phase have been know to reverse after a "short" power blip. The is why they had a delay relay on them.
    Life is too short, Behappy!
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  12. #12
    Join Date
    May 2007
    Location
    Dry as a bone Tucson
    Posts
    4,542
    Dear stumped, maybe it wasnt hooked up right in the first place..................
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  13. #13
    Join Date
    Jul 2005
    Posts
    5,576
    Quote Originally Posted by engineerbrian View Post
    Ok heres one that will stump you. Well it stummped me and my HVAC buddies anyways.

    The lobby unit in our building has been running 24/7 for 3 years with no problems. Then one day out of no where we found the main breaker for the unit tripped. After a quick investigation we reset the breaker and the compressors sounded horrible. we assumed a mechanical failure, but threw guages on it anyways and found the pressures to be equal while the compressor was "running".

    So heres where it gets interesting. The fan is rotating properly, however my boss decided to switch 2 of the 3 legs on the compressor to change its direction and what do you know, the compressor ran perfect!

    Hopefully i gave you guys enough info. So what do you think, were stumped?
    Maybe your boss knew what to do because he was the one who switched them the wrong way before you got there.

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