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  1. #14
    Join Date
    Aug 2012
    I have been scolded for my reply to this post because I don't have the * by my name. So I will go through the proper channels before I post anything else here. Sorry Mods!!

  2. #15
    @dunkman, by "exhaust ducts", I am referring to the hot air exhaust ducts that begin at the ceiling and carry the hot air back to the units. Thanks for asking

    Challenger 3000 - is the make/model of our HVAC units

  3. #16
    @j3hvac - lol, I saw that! Rules are rules, glad I read em so I noticed you lacked that little star. Nevertheless, I appreciate any input and would still love to hear you back up your theories if you can find a way. You seem to know more about HVAC than me, so that's enough to make you qualified in my book.

  4. #17
    Join Date
    Jan 2010
    Central Texas
    I'd expect that the building/house AC is being shut off/back at night. This can cause the increased load in the space, that eventually causes the High Temp Alarms. Check with the Building HVAC guys to see if the Building/House AC is on a schedule.

  5. #18
    Join Date
    Jun 2006
    New Jersey
    Maybe I missing some facts......You are venting supply air from units via ceiling registers(via a upflow ducted challegers). I can get that, but what about the returns? You mention ceiling exhaust openings? Normally you would have a hot isle behind the racks. It would be sealed and returns from CRAC's would pull from.

    What kinda of Challengers are they? Water cooled or air cooled dx? Split or self-contained? Or are they chilled water?

  6. #19
    Join Date
    Dec 2006
    new england
    Dunkman, a challenger is a Liebert unit.
    Chaos equals cash$$$

  7. #20
    Join Date
    Apr 2010
    LIEBERTS! Why didn't somebody say that before? Now I just feel silly. We have a bunch of those around here, none are ducted units though.

    Total of 15 tons, I wonder if you're short on capacity. I'm not real sure how anyone would fix this one over the internet, Lieberts are complex enough in person.

    Personally I would seriously consider purchasing a data logging device that can record temperature so you can look back and verify the actual temp when you get an alarm. You said it feels 71 in there. You might just have a bad temp alarm.

    Another thought, do they have economizers???

  8. #21
    Join Date
    Jan 2004
    By exhaust holes. Do you mean egg crate grilles, and is this a return ceiling plenum?

    As above, put a data logger in there and see if its really reaching alarm temp or if its just a sensor going bad.
    Contractor locator map


    How many times must one fix something before it is fixed?

  9. #22
    Join Date
    May 2012
    San Diego, CA
    If the room is 71 F when the alarm goes off, then I don't think it is going off due to high heat... is there something wrong with the alarm sensor? Or is the alarm sensor both a temperature and humidity sensor? The reason I ask is because low humidity levels lead to static electricity so if your sensor can sense the humidity then your alarm might be going off due to the air being too dry. Just a thought....
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

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