McQuay Centifugal
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  1. #1
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,131
    Chiller guys and gals
    This is one that has been going on for a little while....McQuay R134a machine, Model# PEH087-AAAB
    Serial number S7B81030-00. About 2 or so years ago, the shop got a call on this machine. A tech went out, L1 and L2 600 amp fuses blown. Replaced. Ran for a couple of months. Another tech goes out, L1 and L2 fuses blown. Replaced. This happened a couple more times and I inherited the issue. I cannot say what they found and they have long since left the shop. So, around Nov of 2003, I get my first call on this machine, and by now, I am sure that you have guessed the call.... thats right, L1 and L2 fuses blown. I meggered the motor to ground, showing at or close to infinity,with no phase to phase shorts, checked wires and physical interlock, etc. I did decide to order and change the shorting contactor points, and ran the machine.Didn't have a problem with this machine(that I know of) until recently, when maintenance was being done on the tower and I caught hell trying to get it online with very cold tower water. I made a point to ask the facilities director if the fuses had blown since that last call and he indicated that they had not had a recurrance of this issue....until this morning. So, I get there and L1 and L2 are blown, megger as stated above and check the physical interlock between 1S and 2M, as I did before. I am going to replace it and the other AUX contactors in the course of my trouble shooting and would like some input. Thanks.
    R404a

  2. #2
    Join Date
    Feb 2003
    Location
    Wichita Ks
    Posts
    1,452
    after it runs a while i would check the fuse and wiring with a infrared thermometer to look for hot spots as a poor connection. i would go back to the main breaker also. also you can put a voltage recorder on and see what is happening over time.

  3. #3
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,131
    Freon,
    I think thta is a good idea. I will get the data logger and try it out. The infrequency is what has me going.

    Thanks
    404

  4. #4
    Join Date
    Jan 2005
    Posts
    604
    I do have one thing to say about your megger, if that's as good a reading as you can get, you should maybe get a different one.
    Having said that, you could always rotate L1 to L2, L2 to L3, then L3 to L1. This will keep everything in same rotation. If problem follows your moves then it's a line problem.
    High amps can be caused by low voltage on the feed. I'd check with utility and see if they had problems on particular days.
    Last but not least are the fuses sized properly?

    Eventually whatever is causing the problem will release its encapsulated smoke and you will be able to locate the problem.



    [Edited by r718 on 03-09-2005 at 09:39 PM]

  5. #5
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,131
    good idea on the switching of lines. thanks.
    404

  6. #6
    Join Date
    Dec 2003
    Location
    Kenilworth New Jersey
    Posts
    230
    I don`t know how they prove vane closed at startup with Microtech are they still using vane closed oil pressure switch? Could be sometimes starting with vanes partially open or a bouncing flow switch. Just a thought...

  7. #7
    Join Date
    Feb 2004
    Location
    Kentucky
    Posts
    95

    Frown McQuay chiller blown fuses

    Hold it hold it "Timmy or Jimmy" think about the advice on switching L1 L2 - the compressor will only run in one direction!!!!!!!

  8. #8
    Join Date
    Jan 2005
    Posts
    604
    Yep, ya always got to think about what you read on the internet.
    I guess it's possible if ya switch the line side as follows; L1 to L2, L2 to L3, L3 to L1, that the compressor may change rotation. I'm just not sure on what planet.

  9. #9
    Join Date
    Jan 2004
    Posts
    1,174
    Make sure that your wire size is correct for your machine and length of run from electrical room, it could be sized so close that at high load conditions it over amps the fuses, it could also be a short in the wire running back on the line side.

  10. #10
    Join Date
    Oct 2003
    Location
    tidewater, va
    Posts
    2,131
    Appreciate all of the input. Mathias, I did put a rotation meter on the machine and have not started it yet, I will let the oil warm up first. Like I stated before, I have not had much experience with this style machine and I know LEW2 has,among others. How does this machine assure oil return? I have a unit adjacent this one with a low level of oil in the tank, and I ran it overnight. I have a five degree evap aprroach, 2 degree suction superheat and very little discharge superheat, so I know that charge is not an issue. Today my sump is still low. I put a call in today to get an O/M manual on the machine so I can get a bit more edu-macated


    404

  11. #11
    I have a question, and some suggestions..... is the starter fused? Or, fuses in distribution panel? If fused remotely, I might suspect L1 and L2 get together on occasion. It is also possible that there is an intermittent short between T1 and T2 in the conduit. Next, I would turn off the liquid injection to the compressor and check discharge superheat. It should be around 14 degrees at full load, and go up from there as the load decreases. From the refrigerant side, I suspect the compressor may be seriously flooding back at start-up, although I don't see why it would always pick L1 & L2 fuses to blow. You might also test the vane closed switch for calibration. I would set it to 40 psid. Finally, look closely at the motor terminals for cracks and copper spattering. Thismay be a path to ground, especially when they start sweating.

  12. #12
    Join Date
    Feb 2005
    Location
    Dothan, Al
    Posts
    3,453
    Look for device that is single phase running on L1 & L2 only. Control power transformer, pump motor, etc.

  13. #13
    Join Date
    Aug 2002
    Location
    Southold.calm
    Posts
    5,373
    Check RMS rating on replacement fuses, it may be to low.

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