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  1. #1

    McQuay WMC 290, EXV Sequence of Ops

    I am involved in commissioning plant w/ (3) new McQuay WMC Chillers. We have (2) 290's and (1) 150. One of the 290's is operating outside of what the McQuay IOM's indicate for normal Superheat and Discharge Superheat. The McQuay SU tech adjusted the EXV Gain and Slope during start-up because the EXV was opening/ closing w/o ever leveling out. It is now operating with -10 to -20 degree suction superheat and 5 to -7 degree discharge superheat. How is the EXV controled? The McQuay SU tech was not able to tell me (or he just didn't want to try and explain). I believe the Turbocor compressor cooling line is vented just prior to the suction temperature sensor. How is the refrigerant metered through the compressor? Any input is appreciated. I have not had much experience with centrifical's or Turbocor's.

  2. #2
    Join Date
    Dec 2008
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    You've got something in the electronics that's seriously messed up. It's impossible to have that much negative superheat on either side of the compressor and still operate. Lying sensors, wrong unit of measure programmed in, etc.

  3. #3
    Join Date
    May 2006
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    Quote Originally Posted by klove View Post
    You've got something in the electronics that's seriously messed up. It's impossible to have that much negative superheat on either side of the compressor and still operate. Lying sensors, wrong unit of measure programmed in, etc.
    It's superheated all the way down untill it is saturated. There is no such thing as negative superheat. I was reminded of that in a Parker TXV Training class.........once.!!!!

    Like Klove says, check all your sensors. Trace back the sensor leads to the terminals they are landed on. I've had more than one incidence where they were terminated on opposite circuits on different brands and different styles of machines.
    "Wheel" mechanics work on "Wheel" chillers

  4. #4
    Join Date
    Dec 2007
    Location
    Northern California
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    32
    Cooling line is liquid refrigerant from the condensor to the compressor. Serveral temp sensor can energize 2-solenoid behind the side cover to cool the electronics and motor windings

  5. #5
    Join Date
    May 2001
    Location
    Western Wa
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    1,831
    Make sure you're looking at the compressor that is running.
    God Bless our Veterans

    God Bless the USA

  6. #6
    All of the sensors are integral to each Turbocor compressor. I am looking at the compressor that is running, and checked operation with both compressors operating w/ simular results. I am wondering if there is a chance that the cooling line servicing the compressors is flooding the evaporator inside the compressor, resulting in liquid flashing at the vent port at the compressor suction. McQuay mentions in the IOM's that the suction temp sensor is located downstream of the compressor cooling line termination and reported temperatures can be influenced.

  7. #7
    Join Date
    Nov 2007
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    DownUnder
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    33
    Might be a bit basic but the water is piped up correctly and you have sufficient flow?

  8. #8
    Join Date
    Dec 2008
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    Dixiana, AL
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    Quote Originally Posted by referteacher View Post
    It's superheated all the way down untill it is saturated. There is no such thing as negative superheat. I was reminded of that in a Parker TXV Training class.........once.!!!!

    Like Klove says, check all your sensors. Trace back the sensor leads to the terminals they are landed on. I've had more than one incidence where they were terminated on opposite circuits on different brands and different styles of machines.
    100% correct. I had negative approach on the brain when I made that post. And even negative approach is a very transient condition that only rarely takes place - operation is impossible under those conditions. The part about the sensors was OK, the negative superheat was definitely .

  9. #9
    Figured out part of the problem, had to program the compressors for ambient pressure (14.7#). Still trying to work out some bugs. Seems that this chiller was not set up correctly from the factory. At least we have one that is working correctly that we can compare notes too.

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