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Thread: WMC

  1. #1
    Join Date
    Dec 2005
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    WMC

    Hello,
    I hace a WMC aprox 135 ton single comptrssor. It has been tripping on Low evap pressure. I live in the north and its cool. The tower is controlled from chiller and is single fan driven by VFD. What should the lift be set up to default is 30 i think. Is there a upper limit. I was wondering also if I lower the min amps below 10% as long as I keep motor cooling.

    I would like to raise the lift as the condenser sightglass is full and evap is empty and I think were stacking refrigerant in the condenser. It has tripped off on Low evap pressure a few times.

  2. #2
    Join Date
    Jul 2009
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    In a mechanical room....
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    Whats your super heat and sub cooling? Temp diff across the coil and heat ex barrel?

    As far as the vfd on the motor it all depends on what kind of equipment you have if the tower has a gear drive you spin it too fast or slow are you will ruin the gear drive, how cold is cold?

  3. #3
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    Its a belt driven fan the min speed for the motor is 25 hz and thats our min on the drive. I am runninig a 2oF superheat with approx 1.5 oFTD across the barrel. I set the lift septoint to 45 and my chiller going into alarm has quit.

  4. #4
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    You should see +10 td deg across barrel and 15 deg superheat your not exchanging heat clean the barrel it's prob fouled whats the ref pressures suction must be low, with 2 deg superheat you should be worried about moving oil do you have an oil sight glass check oil level prob all in evap

  5. #5
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    Its Oil free machine im running unloaded about 12%fla on a flooded evap.

  6. #6
    Join Date
    Nov 2008
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    1,673
    For infrequent trips you can hook up an event recorder for solving knotty troubleshooting problems.
    http://www.google.com/search?hl=en&s...&aq=f&oq=&aqi=

  7. #7
    Join Date
    Feb 2003
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    Quote Originally Posted by chrishvacman View Post
    You should see +10 td deg across barrel and 15 deg superheat your not exchanging heat clean the barrel it's prob fouled whats the ref pressures suction must be low, with 2 deg superheat you should be worried about moving oil do you have an oil sight glass check oil level prob all in evap
    A WMC is a McQuay chiller with a turbocor compressor, no oil. 2 degrees is fine for the chiller. The only time he might see 10 degree across the barrel is at full load and if that was design.

  8. #8
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    Jul 2009
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    Well Centrifugal Chillers can be a pain in the a$% as we all know low pressure is different sorry didn't see the wmc thats a mcquay so call em up tell them what you have and they will tell you exactly what to look for.

  9. #9
    Join Date
    Aug 2006
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    Ohio
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    You also might want to run your tower VFD down to 18-20hz min.

  10. #10
    Join Date
    May 2001
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    Western Wa
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    You can probably get away with 15Hz on a fan, which is a variable torque load.

    I service one that is two compressor but also kind of a low load system.

    The tower is VFD fan and the unit is set up on lift rather than entering temp.
    I can't remember exactly sitting here at home, but it seems to me it's set up at 40 or 45.
    You've gotta have enough DP across the compressor or it won't allow the thing to load up, due to the refrigerant cooled compressor, which as I'm sure you're aware, has it's own liquid line for cooling.

    I think you did the right thing, but there's a lot of people much more experienced with the Turbocor stuff around here. It will be interesting to hear their take.
    God Bless our Veterans

    God Bless the USA

  11. #11
    Join Date
    Sep 2007
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    Bay Area California
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    321
    if you can, try increasing the min position on the exv...
    also set the suction alarm limit on the compressor up a little bit...

    Chiller Rob

  12. #12
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    Quote Originally Posted by Randy S. View Post
    You can probably get away with 15Hz on a fan, which is a variable torque load.
    Yikes! Aren't you scared of burning up the motor at that frequency?

  13. #13
    Join Date
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    Depends on the application. Most everybody says 20 Hz as a minimum.
    You'd want to check for overheating, but I've seen it done. The ones I saw it applied on were considerably below FLA at 60Hz. So, you could say that they were already derated for under 20Hz.
    God Bless our Veterans

    God Bless the USA

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