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  1. #1
    Join Date
    May 2018
    Location
    Southampton UK
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    3
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    Forum newly - Hello & a problem with a McQuay Chiller

    Hello and thank you for letting me join this forum.

    Our firm specialise in heavy rebuild of moderate to large chillers typically 300 - 1200 kW.

    Recently we have replaced the Controls upon a McQuay ALS chiller on R407C with three systems, working with another contractor who have undertaken the refrigeration system works.

    The chillers has 3 SAL gate rotor screws, a DX evaporator and air cooled condensers.

    Presently one system is down awaiting some parts, but the other two have been commissioned, but one is exhibiting a strange problem, hence my request for assistance.

    System 1 compressor is working just fine

    System 2 compressor is out of service

    System 3 compressor is suffering a very erratic oil level and keeps tripping on low oil level after a short period of running.

    The level may start in the top sight glass, yet within minutes of a start it is at the bottom of the lower glass, so a drop of 8-10 litres. The oil heater (wrap around type) is working when the compressor is off, so it should not be full of liquid refrigerant.

    The chiller was found derelict / out of service for a couple of years with no advice / knowledge available of its condition when it was mothballed. The primary issue was the Controls system, which Daikin / McQuay we were advised no longer support (old Microtech).

    As UK Distributor for MCS Controls (Florida) we simply designed a new controls system using their excellent kit.

    The chiller is on R407C, operating to provide chilled water ~7oC flow. The load presently is light with other chillers also providing service. When testing the return temperature is typically ~8 - 10oC.

    System 3 was found with no oil, although the compressor was examined and found to be internally in good fettle. Our co -client here has provided a POE68 grade oil and so far has added ~25 litres, with the last fill being 10 litres to the top of the sight glass on the Henry Oil separator / reservoir.

    Within a few minutes of start up the oil level dives to the lower glass where the oil level detector observes this and throws in a trip, for which we have set in 180 second delay (is this too long for a McQuay SAL type screw ?). I have tried forcing the load up and down but this does not seem to improve or worsen the situation.

    After a trip the oil level sometimes restores on its own, or if I force a run by manually setting the trip to OK (I can do this remotely with the MCS Controls through our own RODEM remote access system), I can get the oil level to restore.

    We could add more oil but we are reluctant to do this (25 litres already added). I have the original McQuay manual but this does not advise what the system oil quantity should be, nor even the grade.

    We cannot get a really decent run to establish the sealed suction and discharge superheats. We have weighed in the plated weight of R407C following full pressure tests and evacuation to 2 torr.

    Any ideas ?

    Presently we are thinking this is the Henry separator, but would like to see if others are aware of this problem and how to fix it, or help us diagnose the issue.

    Thanks.

  2. #2
    Join Date
    Mar 2008
    Location
    kansas
    Posts
    407
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    A long shot but is your exv opening?
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  3. #3
    Join Date
    May 2018
    Location
    Southampton UK
    Posts
    3
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    Thread Starter
    Quote Originally Posted by crazzycajun View Post
    A long shot but is your exv opening?
    Seems to be. The driver responds and the suction pressure rises as I would expect.

    There is a pre pump out set up. I could disable this.

    However, the other perfectly working system has identical settings with shared setpoints.

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