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  1. #1
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    117

    Liebert Deluxe System 3 in computer room. low suction??

    Ok I got this Liebert that I keep going back for a low suction pressure alarm. I get there every time and put the gauges on and the pressure looks good before I even start it. And the low pressure switch is closed.(must be auto reset) I have to turn the main switch off and on and it starts up and the pressures look great, sight glass full. I've sat there for long periods waiting for something to happen and found no problem. In the alarm history it seems like it happens maybe 10-12 hours after I reset it sometimes longer. Any Ideas??? maybe liquid line solenoid getting weak and closing after running for several hours. I'm new with these units and could use a little guidance. Thanks, Bill

  2. #2
    Join Date
    Jul 2003
    Location
    Massachusetts
    Posts
    288
    if it's unable to reach a specific humidity level, it will cycle cooling well past it's cooling setpoint. Probably cutting out in the evening when trying to do this?

  3. #3
    Join Date
    Dec 2009
    Location
    Fort Worth, Texas
    Posts
    151
    check heaters. when humidty is high and setpoint is reached, heaters should be energized to temper the air.

  4. #4
    Join Date
    Oct 2005
    Location
    Las Vegas
    Posts
    45
    What type of machine? DX? AG? AM? ICOM? Post the units model number and year of manufacture, with Liebert the model number will say exactly what the machine is & what it has.

    If it was de-humidifying with out re-heats you would set off the low temp alarm before you would get low pressure. On AM or better processors you have an alarm history to check.

    If it's a DX machine with a 2 or 4 fan condenser it's possible (though not likely) if all the fans come on in a low ambient condition (say 70 or lower) that you are pulling the pressures down to far. It's a 30 or 60 second window that the processor ignores the status of the low pressure switch when the compressor starts.

    Whats the setting of the low pressure switch? Cut out & cut in? Is it factory of after market? Factory LP switches do NOT have the adjustment slot for a flat blade screwdriver. Air cooled machines usually run a 30psi cut out, although I have seen 15 psi switches from the factory before (in air cooled machines).

    It's possible the solenoid is sticking, more probable other things are effecting it.

  5. #5
    Join Date
    Feb 2011
    Location
    Sacramento, CA
    Posts
    147
    Quote Originally Posted by rbcsj View Post
    If it's a DX machine with a 2 or 4 fan condenser it's possible (though not likely) if all the fans come on in a low ambient condition (say 70 or lower) that you are pulling the pressures down to far. It's a 30 or 60 second window that the processor ignores the status of the low pressure switch when the compressor starts.

    .
    Are the cfm contactors sticking? Bulb stats on the condenser set correctly and calibrated? Is the Penn 70 fan controller set up and calibrated properly?
    I have done so much with so little for so long, that now I can do almost anything with nothing at all.

  6. #6
    What were your pressures if you don't mind?

    Also, is this an air cooled unit or water cooled?

  7. #7
    Join Date
    Apr 2006
    Location
    mechanical room
    Posts
    1,259
    post more info.

  8. #8
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    117
    Sorry Ive been away from the area. It is a air cooled unit. Suction pressure 65liquid pressure 200 I will get model number tomorrow, Im sure there will be another low suction pressure alarm and the compressor will be shut off and the other compressor will be trying to keep temp. Havent had time to troubleshoot it since my first post.They havent been complaining since theres three other units in the room. Thanks for the leads on what to look at, maybe I'll have time tomorrow.

  9. #9
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    117
    Sorry the suction line is 75psi and the liquid line 240psi
    The model number is fh199a-c00 dated 1991 right now I know one thing, it's not humidifying something is causing the pan not to fill. Got to check it out.

  10. #10
    Those pressures seem to good to be true. Sounds like a faulty Low PSI Switch. They are Auto reset. Only HPS is Manual reset. You could test the LLSV by having guages on and cycle compressor off and see is Suction pressure rises after pump down. If that was the case, this would happen all the time.

  11. #11
    Join Date
    Feb 2011
    Location
    Fogelsville, Pa.
    Posts
    117
    Yea I was thinking the low pressure switch but another tech just replaced it a month ago trying to resolve this same problem. Maybe ill swap the other compressors Lps see if that does anything. Cant see it being bad though. Check back soon. Thanks. btw the pressures are true.

  12. #12
    Join Date
    Sep 2007
    Location
    NC
    Posts
    28
    Do you have the ability to data log pressures, and temps? If so you will see exactly at is happening and when.

  13. #13
    Join Date
    Nov 2005
    Posts
    1,350
    Only one of the compressors is tripping, but both are on the same condenser. That would eliminate the fans not being set up right. Is there hot gas? If so is it working? Is the compressor that is tripping always the first one to come on? Are the starts rotated?
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

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