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Thread: Oil Migration issue

  1. #1
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    Oil Migration issue

    I have a 50 ton two circuit condensing unit for low temp storage. This unit was put in to replace a 40 ton unit, the refrigerant used is 404A, the condensing unit and piping were not replaced. The unit ran flawless for about 6 months then there was a crack in the header manifold at a clamping point. Three times repairs were made to the line that failed, when finally I made the call to have the manufacture replace the header. The unit ran fine for about two months then started tripping off on oil. The two circuits are identical and are independent from each other, the circuit that runs fine is closer to the evaporators by 50' compared to the one that has the oil migration issue. The head and suction pressure 250/20 for both circuits. The circuit with the migration issue starts, the suction pressure drops 3 to 5 psi which I figure is due to the oil migration. One of my techs thinks its a design issue with the piping, or sub cooling (whaaat), could it be because the compressor is starting to fail because of the many times its run with out oil? What do you think?

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    Not nearly enough info.
    Would need log sheet, model numbers, piping iso, cycle rates, etc......

  3. #3
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    40 - 50 Ton ( we deal in HP) yet No piping changes?

    Id have to see this!

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  5. #4
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    In reference to oil migration as you put it, do you actually mean oil return or lack thereof?

    Sent from my SM-G950U using Tapatalk

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    PM me and I will send you a list of about 30 causes of oil loss/low oil pressure.

  7. #6
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    Quote Originally Posted by ehsx View Post
    PM me and I will send you a list of about 30 causes of oil loss/low oil pressure.
    Only Pro members have PM ability, so he can't PM you.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  8. #7
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    Thread makes no sense please come back and clarify what you have.

  9. #8
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    What you describe is not oil migration, it sounds to me to be oil loss...most likely from the multiple header failures. (I assume these were discharge header cracks.)

    What type of compressors and what's the model?

    Do they have an oil level sightglass?

  10. #9
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    Thread Starter
    The unit is made by Century model NDB50L4 and the compressors are Bitzers rated at 102,669 BTUH, the manufacture of the unit was given the original plans of the piping layout and had no input on piping size change. When I say the oil is migrating means it is going to the evaporators and the filters and not coming back. I might buy into a piping issue accept the other circuit has been running fine over a year now, I believe it is either the compressor or some blockage from all the welding repair of the header. At the evaporator they have a sub-cooler and the TXV's were changed thinking they were clogged with debris. I mention the sub-cooler because oil was drained from there, the evaporator and the filter dryers about 4 gallons in all. The line leaving the unit is 1 1/8" and the return in 2 5/8" and transition to feed four evaporators on the condenser unit there is a receiver that functions as a sub-cooler as well.

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  12. #10
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    Quote Originally Posted by Prison dog View Post
    The line leaving the unit is 1 1/8" and the return in 2 5/8" and transition to feed four evaporators on the condenser unit there is a receiver that functions as a sub-cooler as well.
    Someone help me I'm not understanding what's being said here.
    Is it the liquid line is 1&1/8" and suction 2&5/8" ?

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  14. #11
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    W T F is a "Leaving Line & Return Line"?

  15. #12
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    Quote Originally Posted by pecmsg View Post
    W T F is a "Leaving Line & Return Line"?
    .
    Attached Images Attached Images  

  16. #13
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    Is there a possibility of this circuit's oil having a mix of mineral oil and as well as POE, such as if someone inadvertently added mineral oil instead of POE sometime during all of these service repairs?

    I ask because you mention taking a lot of oil out of the subcooler and filter-driers as well as the evaporator. To find a lot of oil on the high side makes me think there may be a problem of oil miscibility such that oil can be stranded in the receiver as well as the evaporators. If this were the case, then there would likely have been a lot more oil still in the receiver that didn't get removed.

    Just a thought.

  17. #14
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    Quote Originally Posted by pecmsg View Post
    W T F is a "Leaving Line & Return Line"?
    I read that to mean liquid line and suction line.... 1 1/8" / 2 5/8"

  18. #15
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    Quote Originally Posted by icemeister View Post
    I read that to mean liquid line and suction line.... 1 1/8" / 2 5/8"
    Or discharge and liquid!

  19. #16
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    Quote Originally Posted by pecmsg View Post
    Or discharge and liquid!
    Discharge on a condensing unit is factory piping within the unit, not liquid and suction which are field piping.

  20. #17
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    Did we determine if it was or wasn't a remote air condenser I didn't look up the model number

  21. #18
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    Quote Originally Posted by VTP99 View Post
    Did we determine if it was or wasn't a remote air condenser I didn't look up the model number
    I A S S U M E D it was from this statement!
    the condensing unit and piping were not replaced.

    Still wondering how you go up 25% in capacity and not change the condenser?

  22. #19
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    Bitzer screw, scroll or recip?

    POE or mineral oil?

    Test % poe with refractometer?

  23. #20
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    Thread Starter
    The Liquid line, high pressure, high pressure liquid, line that goes to the evaporator, small line compared to the larger line, is 1 1/8".
    The Low Pressure Vapor line, big line that goes to the compressor is 2 5/8" everyone clear?

    That was my third attempt to post before it kicked me off in the middle, sorry I didn't prof.

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