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  1. #1

    Confused Fujitsu split unit cycling compressor every 12 hours

    We have a wall-mount Fujitsu Halcyon "Inverter" blower unit in a computer/data room with a 3ish ton condenser in the ceiling above it (between the ceiling tiles and the concrete floor above it). We've been running this configuration for a few years, but recently we installed continuous temperature monitoring for the output of the A/C unit. We noticed it spiking every 12 hours. We observed the behavior in the room first-hand and could actually hear the compressor kicking off and the fan air output reaching room temperature. 3 minutes later, the air started cooling again and back to normal. We've observed the compressor cycling every 12 hours for several days idea how long it's ran this way. It occurs around 1:30 am and 1:30 pm MST within 2 or 3 minutes. If anyone has any experience with such an issue or could provide any insight into what is happening here, it would be appreciated. The fan continues to blow air during the compressor outage, and all timer schedules have been cleared.

  2. #2
    Join Date
    Nov 2005
    need way more info. what temp the room is, dat, rat, etc.
    Those units run all the time whether you think it is or not. The only way to know for sure is to put a amp clamp on it or have the panel open.

  3. #3
    The room runs around 70 F during weekdays and around 75 F on weekends. The A/C unit blows air varying from 43 F to 55 F depending on demand (it's a variable compressor). I'm attaching a graph of the temps in the room over the last ~36 hours. Blue line is A/C output temp (notice the spikes every 12). Red line is room ambient.

  4. #4
    Join Date
    Mar 2004
    Grottoes VA
    Looks like the unit is reseting itself.
    Karst means cave. So, I search for caves.

  5. #5
    Is this normal? How would I troubleshoot this? What could be failing so consistently? Please elaborate. Thanks.

  6. #6
    Join Date
    Nov 2001
    Seattle, WA
    Do you have an emergency generator that tests during those hours? Or any other source of times that could be connected to the power source of this unit?

    One test that you can do as the user is to turn off the power to the unit for a certain time, say one hour for example, turn it back on and see if the resets now follow in line with that one hour off period. In other words the system now does the exact same thing except one hour later. If so the problem is in the unit.
    "The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
    - Alexis de Toqueville, 1835

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