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  1. #1
    Join Date
    Jul 2008
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    Denver, CO
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    Carrier chiller scroll unloading

    I've got a new carrier 30MPW04559A02005 when I get close to my setpoint and the unloader should be enrgized the controller will unload the compressor, then load it back down at thirty second intervals. I was unable to get ahold of anyone in tech support yesterday afternoon at 1630. Go figure! Anyhow does anyone have any idea why the controller is cycling the unloader off and on like this?

  2. #2
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    Jan 2008
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    Dallas ,Texas
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    Are you talking about the digital scroll compressor?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  3. #3
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    Quote Originally Posted by Dallas Duster View Post
    Are you talking about the digital scroll compressor?
    Yes it does have a digital scroll and how far away from setpoint was it?
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  4. #4
    Join Date
    May 2004
    Location
    SE Pennsylvania
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    Capacity control of digital scrolls, normal operation, pulsed output depending on percentage of capacity.

  5. #5
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    Actually this compressor is not driven by a VFD it's just a single speed scroll compressor.

  6. #6
    Join Date
    May 2004
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    SE Pennsylvania
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    Quote Originally Posted by Tiger93rsl View Post
    Actually this compressor is not driven by a VFD it's just a single speed scroll compressor.
    Digital scrolls have their unloaders pulsed off and on at different rates depending on percentage of demand. Values are not right, just an example.

    100% - unloader off
    80% - on 96 secs, off 96 secs
    60% - on 72 secs, off 72 secs
    40% - on 48 secs, off 48 secs
    20% - on 24 secs, off 24 secs

    From Copelands site
    At this stage, let us introduce the concept of a cycle time. A cycle time consists of a "Loaded State" time, and "Unloaded State" time (Figure 2).. The duration of these 2-time segments determine the capacity modulation of the compressor. Example: In a 20-second cycle time, if the loaded state time is 10 seconds and the unloaded state time is 10 seconds, the compressor modulation is (10 seconds x 100% + 10 seconds x 0%)/ 20 = 50% (Figure 3). If for the same cycle time, the loaded state time is 15 seconds and the unloaded state time is 5 seconds, the compressor modulation is 75%. The capacity is a time averaged summation of the loaded state and unloaded state. By varying the loaded state time and unloaded state time, any capacity (10%-100%) can be delivered by the compressor.

  7. #7
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    Quote Originally Posted by Tiger93rsl View Post
    Actually this compressor is not driven by a VFD it's just a single speed scroll compressor.
    Correct the compressor motor runs 100% but the scroll plates internally unload the compressor . Makes a funny sound when it pulses.
    UA 100

    It takes three people to do anything around here. Two do the work, one explains to the crowd of people who showed up when they seen smoke and flames.

  8. #8
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    Jul 2008
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    Thanks guys that explains a lot, I just watched copelands video on digital scrolls. I always thought the digital scrolls were the VFD driven compressors.

    Here is the video if anyone is interested.

  9. #9
    Join Date
    Jan 2009
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    Not in Iran
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    Ok , carrier digital scroll split systems 38ADP
    must have supply and return air temp sensors , if not it will not work properly- also factory insists to have back flow installed- just put in 30 ton, dual circuit --
    RLA is 55, I have seen It go from 52RLA to 30RLA and back and forth - all day-

    Energy efficient.. Not running 52RLA 100% of the time-



    ITs ALL ABOUT THE WORDING- what I mean is that isn't it JUST hot gas bypass????
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

  10. #10
    Join Date
    May 2004
    Location
    SE Pennsylvania
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    929
    Hot gas bypass requires the compressor to constantly compress, with a digital scroll it does not pump when unloaded.

  11. #11
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    Jan 2009
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    Not in Iran
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    Oh - thx for info friend.
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

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