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  1. #1
    Join Date
    Jul 2009
    Posts
    4

    Liebert CRAC unit - short cycle problem

    I'm haveing problems with my liebert with short cycle alarms. I know the alarm triggers when there are 10 starts in a 60 min period... but neither I or my hvac tech can figure out why it's trying to start so much. Anyone here have that problem? or know how to fix it?

  2. #2
    Join Date
    May 2009
    Location
    northern kentucky
    Posts
    143
    Is this a new install or existing? Maybe to big (not enough load) or did you change equipment and not producing as much heat.

  3. #3
    Have your tech check the diff. Settings having them set too close will cause short cycling

  4. #4
    Join Date
    Dec 2007
    Posts
    28
    diff good idea, oversized unit with low load will do it to. if unit has recip comp maybe bad valves, leaking solenoid. or you could be just low on gas. real question is what kind of mechanic do you have working on this?

  5. #5
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,831
    Spread out the dead bands on both temperature and humidity. If the unit is oversized, spread them out more. Allow for the deadbands in the alarm settings, too.
    God Bless our Veterans

    God Bless the USA

  6. #6
    Join Date
    Jul 2009
    Posts
    4
    thanks for the responses.

    The units are about 10 yrs old, in a Data Center. The temp settings are set close to maintain a steady temp... and the other lieberts, 2 other crac and 3 ACU units are all set at the same settings and I don't have this problem with the others.

    Please don't abreviate, I don't know enough about the equipment to know what a "diff" is.

  7. #7
    Join Date
    Jan 2009
    Location
    Paradise, NL, Canada
    Posts
    41
    If this computer room has a raised floor you can also try relocating the floor panels that are floor grills as far away from the unit as possible to minimize short circuiting of air.

  8. #8
    Join Date
    Mar 2005
    Posts
    53
    This is not a site for do it yourselfers. Hire a qualified technician to troubleshoot your problems, It will be cheaper in the longrun. We make a living doing this work, I will never understand the guys on this site so willing to give information out.

  9. #9
    Join Date
    Jan 2008
    Location
    Dallas ,Texas
    Posts
    3,705
    Quote Originally Posted by Hutch View Post
    thanks for the responses.

    The units are about 10 yrs old, in a Data Center. The temp settings are set close to maintain a steady temp... and the other lieberts, 2 other crac and 3 ACU units are all set at the same settings and I don't have this problem with the others.

    Please don't abreviate, I don't know enough about the equipment to know what a "diff" is.
    What`s a crac and what`s a ACU ?
    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.

  10. #10
    Join Date
    Jun 2004
    Location
    Howell, Michigan
    Posts
    16,176
    Quote Originally Posted by thegoodlistener View Post
    What`s a crac and what`s a ACU ?

    CRAC=Computer Room Air Conditioner

    ACU Air Conditioning Unit

  11. #11
    Join Date
    Feb 2007
    Posts
    534
    Quote Originally Posted by Hutch View Post
    thanks for the responses.

    The units are about 10 yrs old, in a Data Center. The temp settings are set close to maintain a steady temp... and the other lieberts, 2 other crac and 3 ACU units are all set at the same settings and I don't have this problem with the others.

    Please don't abreviate, I don't know enough about the equipment to know what a "diff" is.

    There was also a problem with the PC board back then that gave various nusiance alarms, good news is it is reparable call in a Liebert certified contractor or at least one who knows of this problem and how to repair it.

  12. #12
    Join Date
    Jul 2009
    Posts
    4
    Quote Originally Posted by schomaker9253 View Post
    This is not a site for do it yourselfers. Hire a qualified technician to troubleshoot your problems, It will be cheaper in the longrun. We make a living doing this work, I will never understand the guys on this site so willing to give information out.
    Wow.... thanks for that... maybe a message should be put on the site for others looking for infomation "Don't bother coming here unless you already know everything" .

    I AM paying a certified HVAC professional to come in and work on the equipment. I'm trying to see if anyone else had this problem that may help us determine possible causes, at this time, he cannot find the cause.

  13. #13
    Join Date
    May 2001
    Location
    Western Wa
    Posts
    1,831
    Look for differences in locations of supply and return at the different units.
    Check the sensor calibrations. Is the "under floor" more, or less, full of piping and wiring around the short cycling unit? Is there simply less load on this unit due to rack location? Is there house air coming in near the unit?

    Parallel units can be a big pain. But the world is full of them. And each room is different.
    God Bless our Veterans

    God Bless the USA

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