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  1. #1
    Join Date
    Jun 2016
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    Gordo, Alabama
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    Liebert AC for computer room

    I don't have the model # right off hand so don't crucify me please lol, Ok got a liebert unit inside a computer room along with a single fan condensing unit outside, cleaned coils on condensing unit and checked amps/voltage just to rule out condensing unit. the typical temps for this computer room from what I have been told is 70 degrees with around 50 % humidity. Its a downflow unit, there is a window that is tinted and sealed to prevent outside air from getting in and the room has been around 73-74 with 54% humidity. At 60% I get a high humidity alarm and at 80 degrees I get a high temp alarm. Filters have been replaced, both compressors are running continuously, there running R22, pressures are around 75-80 PSI suction, and about 205 head, C2 has a run time of 3,000 hrs while C1 is around 800....I do not have a lot of experience with this type of unit so I have been back and forth in the manual, belts are new and tight, bulbs have been replaced, the coil does not looked stopped up, nothing is really standing out to me visually...No the guy that was working on this unit before, who has moved on to bigger and better things pointed out a 7-8 inch pipe that runs above the return into the drop ceiling, and above the computer processors there is a tile removed and I am guessing its to remove heat from processors I would also imagine that it would be pulling additional heat from drop ceiling, he said that could be hurting the system?? So for all of you that have worked on these systems way more than I have, give me your thoughts, suggestions, I just want to understand , Thanks

  2. #2
    Join Date
    Jan 2014
    Location
    New England
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    From working on Leiberts we used to rotate the compressors to lead/lag pushing in a dial for several seconds to rotate on the control board. Don't remember the menu to do that off hand. What do you control your head pressure with, a on/off pressure stat or an OD stat. or a throttling fan speed control? Does this system have reheat ( electric coils ) to help dry the air if the humidity gets to high? If so is it functioning? You mentioned a particular suction pressure and head if these are two separate compressors what is the head and suction of the other compressor. What was the OD temperature when you had 205 head. To me your a little low on the head and a little high on the suction. If these a semi hermetic or recip. Compressor I would pump down each compressor ( if separate compressors ) to check your valves, you should be able to get suction pretty low, ( may have to jump LPS ) to keep compressor running, then let it sit to see if your suction increases while the compressor is off. Is your indoor coil totally wet, by the elbows end which would be a good indication of your charge, or if the compressor is pumping correctly are they partially dry? Do you have a site glass on this system? How does the single fan OD motor know which compressor to follow to maintain head pressure? If these are lead/lag independent compressors?

    Bulbs have been replaced, those are to boil the water for humidifcation?

    Possible your humidity sensor and or dehumidifier sensor is out of calibration, I believe the ones I've worked on just plug into a board. Do you have spare parts?

    Do you have unloaders on the compressor if so are they working correctly, ( to me your pressures seem a little off )
    Last edited by Bazooka Joey; 06-22-2016 at 04:57 PM.

  3. #3
    Join Date
    May 2016
    Location
    Toronto, CAN
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    They often run hot gas by pass. Make sure the selonoid is de enrgized. Have Had full glass until i took the head of the valve an then its running as a true ac. The hot gas is energized when the pressure drops(winter or low load) but will also pump hot gas in on a low charge, potentially confusing the issue.

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  5. #4
    Join Date
    Apr 2016
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    Parts unknown
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    Also to properly check the charge or charge it you need the condenser fan running all the time so you will need to bypass any speed control and try to do it when it's warm

  6. #5
    Join Date
    Jul 2015
    Location
    South Dakota
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    Is this a dry cooler situation? I highly recommend calling the customer support number that is likely on the unit. They will either walk you through what you need to do or get you in touch with someone who can do it and show you how to do it.

  7. #6
    Join Date
    Jul 2015
    Location
    South Dakota
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    Quote Originally Posted by LSullivan View Post
    I don't have the model # ... , Thanks

    Just want to say, SLOW DOWN AND BREATH!!! I went back and read your only posts to the forum so far and can't help but be reminded of the situation that I found myself in 11 months ago. Took a new job at a local university after doing resi work for several years. getting tossed into an insane world where nothing makes sense and everyone around you is telling you something different, almost all of it being wrong. Stick wit these guys here at HVAC-talk, they love guiding us young bucks into doing the right thing the right way, so you've made a great first step. and if your boss asks you why you're looking at your phone in the morning, just give him my number....

  8. #7
    Join Date
    Jan 2014
    Location
    New England
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    Yes as already suggested call Liebert, they may have a sequence of operation and a troubleshooting guide or Technical Services may be able to help or they may refer you to a Liebert Distributor in your region.

  9. #8
    Join Date
    Feb 2010
    Location
    Calgary, Alberta
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    There's too many variables to consider without having a model number and unit specifics.

    Liebert tech support is fantastic, but have your meter handy and all pressure readings. Don't waste their time by not being prepared!


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  10. #9
    Join Date
    Jan 2012
    Location
    Montreal, Canada
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    The boys in Columbus are great. Get all your info and give them a call . Followed a training with one of them. Very knowledgeable.
    Check the hot gas bypass .

  11. #10
    Join Date
    Jul 2008
    Location
    Nova-Scotia, Canada
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    High suction and low head. Bypass should only really come on about 57-58.... I'd peek around and see how hot the discharge is as well as the suction. Is it a recip?

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  13. #11
    Join Date
    Jan 2015
    Location
    Iowa
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    Check your humidifier could be stuck "On" Depeding on year/model there could be 3 different kinds on this machine

  14. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
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    Change the humidity from relative to absolute and see if it goes down.

    Sometimes this little trick helps. A 75-80psi suction is not going to get your coil wet enough to lower humidity.

    Raising the temp will also lower the humidity if the stat is set to read relative.

    They have probably added some more load and the room leaks.

    75-80 / 205 head seems low like the compressor is weak. Unless it was cool outside.


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  15. #13
    Join Date
    Dec 2004
    Location
    Chicago area
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    If Im not mistaken, 205 is what the head pressure control valve for low ambient maintains. Id bet your are low on charge. 2 compressors means 2 circuits with liebert. There should be a LL sight glass on each circuit. If the unit is what I think it is, then its about 5 feet wide?
    If so, when facing the compressors, to the right there are the liquid line driers and LL sight glasses. You may need to remove a door to see them.
    Also, the one fan condensers normally have a receiver on each side for each circuit. There should be a sight glass on those also with little red plastic floats so you can easier see the level. The receiver level should be just to the upper liquid glass.

    I could help more. If I knew more of what you have.

    Good luck.


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