Results 1 to 11 of 11
  1. #1
    Join Date
    Dec 2004
    Posts
    440
    Hey there,

    Should TXV superheat be adjusted if you have an
    extra long run (say 120 feet) to the condensor
    unit. I would say you need less superheat at
    the evap. exit if you have 120 feet run back to
    the compressor, and 100 feet of that run is
    outdoors. Too much superheat at compressor
    can damage the compressor because most compressors
    need cool refrigerant to cool their windings.

    It seems to me in such circumstances the standard
    superheat setting on the TXV should be adjusted
    downwards, but to what value?

    Cheers,
    Michael

  2. #2
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    I havn't seen a piece of residential equipment in a long time that came with a TXV that was field adjustable with the system in operation.
    All of them I have seen in in recent years are factory set, you would have to pump the system down or recover the refrigerant to make an adjustment to the spring tension.

    If the lines are sized properly for the equivelent length and lift, and insulated properly, there won't be an issue with the compressor not being cooled properly.

    I know of at least one application where 10 residential split systems were used that have refrigerant lines with equivelent lengths of up to 230', and the condensors are about 100' higher than the air handlers. No traps in the lines, just solenoids and lines sized to keep the refrigerant velocity high enough to lift the oil, and equipment selected to account for the capacity loss. All of those systems have been running for 10+ years with no compressor failures.
    If more government is the answer, then it's a really stupid question.

  3. #3
    Join Date
    Dec 2004
    Posts
    440
    Hi Mark Bessier,

    Who says the TXV has to be adjusted while the
    system is operating. If I am installing the
    air handler, it has no charge. Nothing needs
    to be pumped down. I am talking about the
    installation of a new system.

    Adjustable or not, TXVs from the factory are set
    for a superheat for runs no longer than 50'. If
    the line-set runs outdoors for more than twice
    that length, won't the refrigerant pick up heat
    as it travels, and reach the compressor a little
    hotter than design temperature? Couldn't a TXV
    with a lower superheat setting correct for this?

    Now, you addreess another issue I have. It can
    be difficult to size the lines properly in such
    a circumstance. If the suction line is too small,
    you have too great a pressure drop. If the suction
    line is too large, you don't have sufficient
    velocity to return the oil. I wonder how you would calculate suction line size.

    Where can I find the formulas for pressure drop,
    and refrigerant velocity?

    You bring up still another issue I am trying to resolve.
    Do horizontal lines have to have a 1/2" / 10 foot
    downward pitch to the compressor to faciliitate oil
    return? What if the compressor is on ground level, and
    a horizontal line runs underground. Would you install
    such a line with any pitch?

    If the compressor is on ground level, and lines must
    make a 20'underground horizontal run won't some oil
    get trapped in the underground line? Won't oil
    adhere to the sides of the line?

    If I have an extra long run and use larger than
    normal diameter lines to compensate for the extra
    long run do I need to add extra oil? I would
    think so. How much extra oil should I add?
    I will certainly need to add extra refrigerant.

    What kind of solenoid are you talking about that
    increases refrigerant velocity? Did I misunderstand
    you?

    Finally, can I slightly reduce the diameter of
    last ten feet of suction line to increase velocity
    to help oil return, if by doing my pressure drop
    remains in specs?

    How can we know if a compressor has the correct
    amount of oil without turning the compressor
    upside down, draining out the oil, and measuring
    the oil volume? Can you even get all the oil
    out of compressor this way? Would you even
    want to expose hydroscopic R-410a oil to air?

    Cheers,
    Michael

  4. #4
    residential system do not normally come with txv, usually axv are what you have. Really smart decision.
    When adjusting a txv however you have to adjust to satisfy more than one condtion. subcooling has to adjusted as the superheat is adjusted, therefore refrigerant has to be added or removed as the txv is adjusted to maintain proper subcooling and superheat values.

  5. #5
    Join Date
    Feb 2004
    Location
    michigan
    Posts
    677
    Originally posted by airworx
    residential system do not normally come with txv, usually axv are what you have. Really smart decision.
    When adjusting a txv however you have to adjust to satisfy more than one condtion. subcooling has to adjusted as the superheat is adjusted, therefore refrigerant has to be added or removed as the txv is adjusted to maintain proper subcooling and superheat values.
    All the 13 SEER coils I've seen have TXV's on them. Have'nt seen any with auto valves.
    I am the "Wally". All others are meer imitations of the original.

  6. #6
    Join Date
    Dec 2004
    Posts
    440
    I would adjust the TXV before installation for
    slightly less superheat. Then charge the
    normal way.

  7. #7
    Join Date
    Feb 2005
    Location
    Miami, Fl.
    Posts
    3,559
    Cobalt,

    This thread, and the others you posted in the residential forum, it seems you are still looking for info on how to install your system at your home. I hope that is not the case, as this is the wrong internet forum for that.


  8. #8
    Join Date
    Oct 2003
    Location
    Valdosta Ga
    Posts
    847

    Hmm

    thats a good point why can't they drill a hole in the bottom of the compressor so it does not have to be turned upside down?

  9. #9
    Join Date
    Oct 2003
    Location
    Valdosta Ga
    Posts
    847

    Hmm

    I was working with a crew one time and found three of the four man crew chasing this guy with a wrench's
    It seems the guy they where chaseing had calculated three strands of winch cable out of 15 would be ok He was lowering a large container with this defective cable that the three guys did not know about till it got to them.
    I would make sure what ever you plan do check with someone qulified before you do it.

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,818
    And how will you knlw what you adjusted the super heat to, untill you run the system.

    If you adjust the Sh too low, you will lose cooling capacity.

    Several manufacturers have piping sheets to figure your piping size, and pressure lossses.

    Trane has a good sheet.



    As arpa says, it sounds like your trying to figure your condo unit out.
    Contractor locator map

    How-to-apply-for-Professional

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

  11. #11
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,031
    Unfortunately, due to site rules the Professional members cannot discuss technical issues with the general public.

    Thank you for your cooperation. This thread is closed.

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