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  1. #1
    Join Date
    Oct 2018
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    With charging superheat gets very low and subcooling still low too for a TXV SYSTEM

    Initial readings before charging : R-410A
    Suction pressure 118 psig
    Liquid pressure 330
    Subcooling 0.9 degrees
    Superheating 27 degrees
    Suction line Temp 67 F
    Liquid line Temp 102 F

    After adding 3 lbs of Freon
    Suction pressure 128
    Liquid pressure 349
    Subcooling 2.4
    Superheating 2 ???????
    Suction line Temp 46
    Liquid line Temp104

    From my Knowledge TXV should start closing reacting to suction line lower Temperature causing less refrigerant flow rate and that will cause the liquid line pressure to start getting higher due to refrigerant accumulation in the liquid line and spending longer time in the condenser Coil and release more heat and get higher subcooling . When TXV closes less refrigerant will be allowed to the Evaporator coil and the higher superheat .. so in my case how can superheat gets as low as 2 degrees and the subcooling still doesn't exceed 2 degrees ???
    Notice .. Suction line Temperature changed from 66 F to 46 F
    Factory recommendation subcooling 8 degrees +/- 3
    Trane Condenser unit
    4TRR6048J1000AA
    18341M3P2F

  2. #2
    Join Date
    Oct 2016
    Location
    Clearwater, Florida
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    How long was the 3 lbs in the system before you measured this?

    As you add refrigerant to a running system through the suction line where your clamp is, it can get very cold and so the SH tends to drop out the bottom as you add refrigerant.

    When the TXV senses a colder temperature in the outlet of the evap, it will close to prevent flooding, if the TXV is not reacting, then it's bad. It has 1 job, to maintain superheat, that's it.

    SH shouldn't vary too much, it should be set by you between 20*-40* for most units, I prefer 20-30 personally and it should remain there regardless of the amount of SC you have, as you need more refrigerant, the TXV opens up more as the heat load is high, then as it lowers the temp, it will throttle down and the SH will remain the same.

    SH is not based on volume, it's based on temperature, so quantity of refrigerant is irrelevant, it's the temperature and pressure of the refrigerant which matters.

  3. #3
    Join Date
    Nov 2011
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    USA
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    Faulty TXV...non-adjustable?

  4. #4
    Join Date
    Jul 2013
    Location
    Richmond, VA
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    How much time did you let it run? Sometimes it'll take 10-15 minutes for a TXV to adjust properly. Also be mindful of where your probes are on the suction line because if you're adding liquid refrigerant in, it boils off and cools the suction line near the probe.

    How's your airflow?

    If airflow checks out, look at where the sensing bulb is. If it's a Trane coil, it'll probably be in right place, but I've seen them outside the air handler/coil not secured properly which allows the TXV to overfeed.

    If the TXV sensing bulb is placed properly, TXV needs to be replaced.

  5. #5
    Join Date
    May 2018
    Location
    South Central Wisconsin
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    Quote Originally Posted by CircusEnvy View Post
    How much time did you let it run? Sometimes it'll take 10-15 minutes for a TXV to adjust properly. Also be mindful of where your probes are on the suction line because if you're adding liquid refrigerant in, it boils off and cools the suction line near the probe.

    How's your airflow?

    If airflow checks out, look at where the sensing bulb is. If it's a Trane coil, it'll probably be in right place, but I've seen them outside the air handler/coil not secured properly which allows the TXV to overfeed.

    If the TXV sensing bulb is placed properly, TXV needs to be replaced.


    X2 for sure. Charge adjustment needs 15-20 minutes to balance out depending on lineset length. No numbers until it has time to balance out

  6. #6
    Join Date
    Oct 2018
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    Thread Starter
    Quote Originally Posted by Olivero View Post
    How long was the 3 lbs in the system before you measured this?

    As you add refrigerant to a running system through the suction line where your clamp is, it can get very cold and so the SH tends to drop out the bottom as you add refrigerant.

    When the TXV senses a colder temperature in the outlet of the evap, it will close to prevent flooding, if the TXV is not reacting, then it's bad. It has 1 job, to maintain superheat, that's it.

    SH shouldn't vary too much, it should be set by you between 20*-40* for most units, I prefer 20-30 personally and it should remain there regardless of the amount of SC you have, as you need more refrigerant, the TXV opens up more as the heat load is high, then as it lowers the temp, it will throttle down and the SH will remain the same.

    SH is not based on volume, it's based on temperature, so quantity of refrigerant is irrelevant, it's the temperature and pressure of the refrigerant which matters.
    The last readings was after I charged the system and let it run more than 15 minutes .. and I agree with your explanation superheat should Not go very low like that by adding Freon it should stop at one point and stay constant no matter what.. adding more Freon after this point should only increases the subcooling .. and this is what drives me crazy .. that superheat keep going as low as 2 degrees and subcooling barely increases .. and I can't keep adding Freon because I might risk the compressor by sending refrigerant that is not superheated and part of it may still be liquid and didn't boil in the Evaporator coil . I feel like the TXV wasn't reacting it was just wide open so the more freon I add the less temperature the evaporator coil get. And because it's wide open the liquid refrigerant doesn't get a chance to accumulate in the condenser unit .. that's my guess .. but system is only one year old .. you think it could be a faulty txv ?

  7. #7
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    Oct 2018
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    Thread Starter
    Quote Originally Posted by Saturatedpsi View Post
    Faulty TXV...non-adjustable?
    I think so too about the TXV .. I just didn't check it to be honest So I don't know if it was adjustable

  8. #8
    Join Date
    Oct 2018
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    Thread Starter
    Quote Originally Posted by CircusEnvy View Post
    How much time did you let it run? Sometimes it'll take 10-15 minutes for a TXV to adjust properly. Also be mindful of where your probes are on the suction line because if you're adding liquid refrigerant in, it boils off and cools the suction line near the probe.

    How's your airflow?

    If airflow checks out, look at where the sensing bulb is. If it's a Trane coil, it'll probably be in right place, but I've seen them outside the air handler/coil not secured properly which allows the TXV to overfeed.

    If the TXV sensing bulb is placed properly, TXV needs to be replaced.
    Right .. my probes was very close to the suction service port .
    I let the system run more than 15 minutes before I take the readings

  9. #9
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    Oct 2018
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    Thread Starter
    Quote Originally Posted by joe_arsenal View Post
    X2 for sure. Charge adjustment needs 15-20 minutes to balance out depending on lineset length. No numbers until it has time to balance out
    I gave it more than 15 minutes before I took the readings

  10. #10
    Join Date
    May 2018
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    South Central Wisconsin
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    Quote Originally Posted by gkboghdady View Post
    I gave it more than 15 minutes before I took the readings

    If airflow is within range, change that txv. It seems like it’s not moving

  11. #11
    Join Date
    Oct 2016
    Location
    Clearwater, Florida
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    Check the TXV and make sure the bulb is secured properly, it doesen't sound like it's responding which means it's either not reading the correct temperature or it's broken.

  12. #12
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    Oct 2018
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    Quote Originally Posted by joe_arsenal View Post
    If airflow is within range, change that txv. It seems like it’s not moving
    agree

  13. #13
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    Oct 2018
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    [QUOTE=Olivero;25781604]Check the TXV and make sure the bulb is secured properly, it doesen't sound like it's responding which means it's either not reading the correct temperature or it's broken.[/QUOTE

    agree

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