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  1. #14
    Join Date
    Dec 2010
    Location
    Palm Beach,Fl.
    Posts
    955
    During a very brief power interruption (brown out) the expansion of gas in the compressor can start moving the rotor in reverse. If power is applied during that rotation it is possible for the motor to start running backwards until it overheats and it can do damage to the scroll. It can't pump so the motor isn't cooled by the suction vapor anymore. I had heard that Copeland fixed this issue at some point, but I still see it on equipement built in the last 5 years. For the record, I have only seen this happen to Copeland scrolls.
    Quote Originally Posted by k-fridge View Post
    The laws of physics know no brand names.

  2. #15
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,907
    Quote Originally Posted by SoFlaDave View Post
    During a very brief power interruption (brown out) the expansion of gas in the compressor can start moving the rotor in reverse. If power is applied during that rotation it is possible for the motor to start running backwards until it overheats and it can do damage to the scroll. It can't pump so the motor isn't cooled by the suction vapor anymore. I had heard that Copeland fixed this issue at some point, but I still see it on equipement built in the last 5 years. For the record, I have only seen this happen to Copeland scrolls.
    I'm with Dave.

    I'd take the proactive step of installing a time delay.

    For me, the "loud compressor" you mentioned right out of the box, along with the pressures, suggests to me it is getting started in the wrong direction. A time delay will help inhibit that effect.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  3. #16
    Join Date
    Mar 2003
    Location
    austin
    Posts
    264
    Quote Originally Posted by timebuilder View Post
    I'm with Dave.

    I'd take the proactive step of installing a time delay.

    For me, the "loud compressor" you mentioned right out of the box, along with the pressures, suggests to me it is getting started in the wrong direction. A time delay will help inhibit that effect.
    Thougjt the visionpro stat had a time delay but it very well could be disabled. Thanks.
    when life throws me a banjo, i play it

  4. #17
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,907
    Quote Originally Posted by michigan1 View Post
    Thougjt the visionpro stat had a time delay but it very well could be disabled. Thanks.
    It has it, and it is adjustable in installer setup.

    BUT, it works based on when it (the stat) turns the compressor off ITSELF, or when it "wakes up" from a full power down.

    If power is lost, the backup batteries don't let the stat know the compressor stopped, so it will come back on as soon as power is restored.

    I think the time delay is a better choice than taking out the batteries, as most HO's would not like to have to reprogram the stat for time whenever the power goes off.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  5. #18
    Join Date
    Jul 2012
    Location
    Baton Rouge Louisiana
    Posts
    175
    I had one do that same exact thing tuesday. 11 year old Ruud 3 ton. Except it was running great, good pressures, subcool, superheat, delta T. It never shut off. Pressures went to about 200/275 compressor got REALLY hot. Was rated for 16.5 amps and was pulling 11.5 on one hot leg 3.5 on another. It had a leak in the evap coil and HO just wanted a whole new system

  6. #19
    Join Date
    Apr 2012
    Location
    Paper Street Soap Company
    Posts
    2,304
    What about installing a 5-2-1 on the unit ? Wouldn't it increase starting torque ?

    Also a delay on make timer is cheap too if you want a no fail delay.

  7. #20
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,708
    older scrolls had a habit of starting up and running backwards due to a momentary loss of power. newer ones are not supposed to do that but it sounds like yours might be.
    i would try putting a delay on break timer right before the contactor, only needs to be set for 15 seconds or so to prevent reverse running from happening.

    something to try and much easier than a txv.

  8. #21
    Join Date
    Jan 2011
    Location
    Massachusetts
    Posts
    81
    I had a Ruud 2 1/2 split system in a attic have same problem it was last year new install came out 2times with scroll running backwards hard to find what was causing problem it was the condensate overflow switch I wire at pan it would open for about 2 seconds then come right back on replaced the switch alls ok

  9. #22
    Join Date
    Jun 2005
    Location
    Louisville, KY
    Posts
    389
    I usually wire the condensate safety switch to break R. 99% of the time I install a stat powered by equipment x-former. In the case of an erratic float it should cause the stat delay to come into the equation and prevent the compressor from restarting immediately. In the case of a more static obstruction in the condensate drain, it also makes for an obvious indication to the HO that there is a problem if the stat has no display.

  10. #23
    Join Date
    Aug 2012
    Location
    Tennessee
    Posts
    67
    Sounds like a restriction problem to me, like expansion valve or TXV is "metering" instead of flowing or even a liquid line solenoid valve bad

  11. #24
    Join Date
    Apr 2004
    Location
    Des Plaines,IL
    Posts
    1,012
    Quote Originally Posted by timebuilder View Post
    It has it, and it is adjustable in installer setup.

    BUT, it works based on when it (the stat) turns the compressor off ITSELF, or when it "wakes up" from a full power down.

    If power is lost, the backup batteries don't let the stat know the compressor stopped, so it will come back on as soon as power is restored.

    I think the time delay is a better choice than taking out the batteries, as most HO's would not like to have to reprogram the stat for time whenever the power goes off.
    I think you can solve this problem by hooking up the C terminal to the common on the 24V. When power is lost, the compreesor is "locked out" and won't start up until the lockout delay in the thermostat is satified.
    Stuart
    Lack of airflow destroys compressors.

  12. #25
    Join Date
    May 2011
    Location
    Ripley, WV
    Posts
    1,149
    Is this a HP? If so maybe check the defrost switch too. If it came from the factory with a switch stuck closed it would shut down the condenser motor, get it bypassing and when it comes out of defrost on time could be leading to what you are seeing.

  13. #26
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,907
    Quote Originally Posted by mcewans View Post
    I think you can solve this problem by hooking up the C terminal to the common on the 24V. When power is lost, the compreesor is "locked out" and won't start up until the lockout delay in the thermostat is satified.
    That is not what I have seen in the field.

    Of course, the least expensive installer bid for a commercial job means that a C wire is rarely provided, so in that situation, the point is moot.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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