Compressor tripping on thermal overload
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  1. #1
    Join Date
    Sep 2002
    Posts
    510
    I changed out a 2-1/2 ton condenser, an old G.E. cube with a 2-1/2 ton Concorde.
    The line set consists of 1/4" liquid line and 5/8" suction line.
    The indoor evaporator has a TXV on it.

    245psig high side =117°,112°liquid line temp.=5°subcooling.
    66psig low side= 38°,65° suction line temp.=27°superheat.

    14 RLA

    L1=12.20amps
    L2=9.00amps

    90° outside temp
    77° inside temp

    Have to cool the compressor off with a water hose to get it to start.

    any help would be appreciated.

  2. #2
    Join Date
    Sep 2004
    Location
    Memphis
    Posts
    2,502
    Does the a/c have a hard start kit on it? Normally when a coil has a txv instead of a piston for a metering device you have to put a hard start on it. Its starting under a load instead of starting with equalized pressures. My company doesnt do that many txv's so i'm not really up on em. I think this is all accurate though. Good Luck with it.


  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,616
    If the compressor is a recip, do you have a hard start kit on it.

    Is the new condenser listed for 1/4" x 5/8" lineset, or do the install instructions want a larger lineset.

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  4. #4
    Join Date
    Nov 2000
    Location
    Eastern PA
    Posts
    68,923
    It sounds like it is undercharged. If that TXV is set for 27º superheat, it is most likely open too much for the new condenser. Also, if the indoor coil was not changed out, the new system filter/drier is most likely partially clogged.

    Not to mention the strain that the small refrigerant lines are putting on the system.
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  5. #5
    Join Date
    Nov 2000
    Location
    Upstate, SC
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    2,919
    You say you have to cool the compressor with water to get it to start, but what stops it? If it is overheating and going out on overload, then I'd try to get that superheat down to around 12º to 14º and recheck. If it cycles and will not start back, then the start assist may be the ticket along with adding some charge. Either way, that 1/4" liquid line caught my eye. Ain't that awful small for a 2.5 ton system?

    Bobby

  6. #6
    Join Date
    Oct 2004
    Posts
    3,400
    Originally posted by cobitech

    L1=12.20amps
    L2=9.00amps
    Why the imbalance?

  7. #7
    Join Date
    Sep 2002
    Posts
    510
    I think the liquid line is too small. I added charge trying to get the superheat down and increased the subcooling. I had 22°of superheat and 24°degrees of subcooling.
    It still tripped out on thermal overload. I think I may have to change the liquid line out at least to remedy this situation.

  8. #8
    Join Date
    Nov 2000
    Location
    Upstate, SC
    Posts
    2,919
    Apparently you are restricted somewhere if the subcooling is up to 24º and the super heat only dropped 2º. I would have expected the sh to come down more than that, but it very well could be that liquid line. Are there any driers there? How about a strainer at the TXV? It appears we aren't getting enough cooling back to the compressor what ever the reason. Does the indoor coil have a model number?

    Bobby

  9. #9
    Join Date
    Dec 2003
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    Location!, Location!
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    How long is the lineset? 1/4 X 5/8 is too small for a 30K-
    Here's a chart 4 u:
    http://www.rsl.ca/PDFS/technical/rec...e%20sizes'

  10. #10
    Join Date
    Nov 2004
    Location
    South Carolina
    Posts
    9
    Long story in a short version....if it is tripping on thermal overload...then not enough COLD freon is getting back to the compressor...either TXV...or coil...make more measurements to find out which

  11. #11
    Join Date
    Mar 2004
    Posts
    20
    Would someone answer bwal2.I want to know also.Thanks!

  12. #12
    Join Date
    Sep 2002
    Posts
    510
    5/16" liquid line, is what I meant to say. Going back this after noon.

  13. #13
    Join Date
    Feb 2004
    Location
    Maine
    Posts
    483
    Originally posted by cobitech
    I think the liquid line is too small. I added charge trying to get the superheat down and increased the subcooling. I had 22°of superheat and 24°degrees of subcooling.
    It still tripped out on thermal overload. I think I may have to change the liquid line out at least to remedy this situation.
    Ok guys, slow down a bit and think this through. This system has a TXV on it, the job of a TXV is to meter liquid refrigerant into the evap and maintain a constant superheat at the evap outlet. At 24º subcooling you are overcharged, and the TXV is doing it's job of keeping the superheat constant. Try to adjust your TXV until you get around 12º of superheat. Next check your subcooling, adjust refrigerant charge until you get 12º of subcool. The subcool and superheat values I listed will get you in the ball park, however you still need a chart from the manufacturer to dial in the correct charge. Be sure to measure the temp on your discharge line, I bet it's above 250ºF. If you can't get your superheat to come down by adjusted the TXV and still maintain 10-12º of subcooling, you have a restriction somewhere, ie filter drier. High superheat and high subcooling indicates a liquid line restriction. Hope this helps.

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