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  1. #1
    Join Date
    Jun 2004
    Posts
    247
    I am having a new condenser and coil installed. The local HVAC company has decided on a 3 ton Trane (2TTR036) condenser with a 3.5 ton Trane (THX041) coil.

    I have read about TXV metering devices being more efficient but he said with the coil being larger than the condenser a piston will be fine since there will never be too much R-22 to the coil. A TXV would never close, he said. Is he right??

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,850
    Originally posted by wendel
    he said with the coil being larger than the condenser a piston will be fine since there will never be too much R-22 to the coil. A TXV would never close, he said. Is he right??
    You need to find yourself another A/C Company.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  3. #3
    Join Date
    Jan 2002
    Location
    Ft.Worth,Tx
    Posts
    4,584

    Thumbs down

    THXO41A4HPA----44,000BTU-Cooling Flat--.067 Piston

    Have him order :TAYTXVA0E5C-Single Direction Flow

    Ask him to check the rating of that coil with and without txv..
    http://www.ari.org
    "Everyday above ground, is a good day".
    "But everyday that you have made a difference in someones life, may insure you stay above ground a little longer".<aircooled>

  4. #4
    There are 3 conditions a coil can assume;
    1-Flooded
    2-Normal
    3-Starved
    Either type of metering device can control refrigerant to maintain proper superheat and subcooling.
    The TXV is a more precise regulator of refrigerant flow, however I've never had to replace a flowrater piston due to failure and I can't say that about a TXV.

  5. #5
    Join Date
    Nov 2004
    Location
    Thibodaux, LA
    Posts
    1,170
    Originally posted by chillbilly
    There are 3 conditions a coil can assume;
    1-Flooded
    2-Normal
    3-Starved
    Either type of metering device can control refrigerant to maintain proper superheat and subcooling.
    The TXV is a more precise regulator of refrigerant flow, however I've never had to replace a flowrater piston due to failure and I can't say that about a TXV.
    I agree with your statement. The majority of systems we install contain TXVs. Although, I always feel comfortabe with an orfice because it should not fail. Less mechanical parts could possible save a call back.

    If the contractor is reputable and you know he does clean installs I don't see any problem.

  6. #6
    Join Date
    Dec 2002
    Posts
    9,871

    I agree

    Originally posted by mrbillpro
    Originally posted by wendel
    he said with the coil being larger than the condenser a piston will be fine since there will never be too much R-22 to the coil. A TXV would never close, he said. Is he right??
    You need to find yourself another A/C Company.
    1. Why is he installing an unmatched system?

    2. A txv provides a consistent state in the evaporator. A piston is dependent upon outside ambient temp thereby giving a broad swing in superheat.

  7. #7
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,850
    Originally posted by wendel
    he said with the coil being larger than the condenser a piston will be fine since there will never be too much R-22 to the coil.
    That statement above is true! my question would be will there be enough R-22 on a very hot day and how much flash will you have.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  8. #8
    Join Date
    Dec 2003
    Posts
    1,195
    A properly installed TXV with a filter in line just ahead of it will last as long as the rest of it, barring abuse or the always possible flaw. The electrical components will get replaced several times before a well installed TXV.

    I personally can't imagine installing a coil without one. A piston is just a cheaper way to almost do the same job. Maybe up north it doesn't matter, but in the humid south, it makes all the difference in the world. Oversized evap coils are NOT the answer.

    Just ask air1...
    "That's good enough..." usually isn't.

  9. #9
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    763
    oversizing the coil in my book is ok if you don't go over 1/2 ton. Goodman puts 5 ton coils on 2 1/2 ton units, to get their SEER rating up. You should with that coil get 13 SEER as far as I can tell and putting an expansion valve on it doesn't Seem to enhance that coil much. Have your dealer give you the ARI printout on the SEER Rating. Tell him you want to achieve 13 SEER with that unit and he should do that for you.
    Remember if you add an expansion valve the cost will most likely go up. They aint the cheapest thing. Everything costs money. But you should be ok with what you have, The 4TTR seems to have 13 SEER and I could not find the listing on the 2TTR but should be the same I think.
    Good luck.

  10. #10
    Join Date
    Oct 2004
    Location
    Texas
    Posts
    1,172
    I just have to chime in here. Forget the seer rating. Match the evaporator coil size to the condensing unit. YES YES to installing a TXV. TXV is not that much extra. Get another contractor or insist on txv. A piston does not monitor and adjust the refrigerant feed into the evaporator coil, it is meerly an orifice that lets refrigerant into the coil with no consideration as to what the system requirement is. A txv will monitor the load of the evaporator coil and make adjustments to maintain the ideal refrigerant flow. Dont listen to these guys that tell you about txv failure. It happens, but to a dagree that it is a non issue. Make sure when you choose the txv you also have the factory hard start kit installed. It is installed in the outdoor unit and provides the needed boost to the compressor on start up.
    Saddle Up!

  11. #11
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,770
    You'll get better humidty removal with the txv, that means better comfort.


    I don't know if anybody here remmembers the old thermopride a/c's, they always used txv's.
    Only had a problem with flash if they were under charged.

    Have your hvac guy check the rating of youor coil for latent heat with a piston, and with a txv, he'll see why to use the txv.
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  12. #12
    Lots of good advice here. Ill just add, that, using a TXV generally allows you to run the cooling at a lower outdoor temperature than a fixed orifice ; a TXV is better for low load conditions . As far as mis-matching is concerned, it is generally acceptable to size the CoolingCoil by a half ton more, although, the suction temperature will be higher due to the imbalance...and dehumidificaton could suffer somewhat.

  13. #13
    Join Date
    Apr 2004
    Posts
    10
    I agree with "Air of Honesty" completely. I can't imagine not using a TXV especially if you live in a humid area of the country. With a piston it takes too much of a cooling cycle before the evaporator gets fed enough refrigerant to start effectively removing moisture. With a TXV, it will open up at the beginning of the cycle which allows good moisture removal throughout the entire cycle. Remember, a TXV's job is to maintain superheat and it will get to that superheat setting fairly quickly. A piston will allow a wide variation in superheat that always starts out high and comes down throughout the cycle.

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