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Thread: Weird readings

  1. #1
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    Weird readings

    I'm working on a 5ton r410a residential split system.
    Sst 28
    Suction temp 58
    Liquid sat 98
    Liquid line 86
    Outdoor ambient 76
    Supply pressure .1
    Pressure before coil .3
    Return pressure. 3
    Indoor ambient 77
    Return temp 76
    Supply temp 56
    Temp before coil 76
    Zone controlled system, these readings are with all dampers wide open and barometric relief damper open partially.

    I'm not sure why my saturation is soo low with my pipe tempurature slightly low as well. I feel like my expansion valve is starving the evaporator, just want to be sure before I replace, if my valve is starving shouldn't my line temp be higher?

  2. #2
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    Looks like you are low on airflow.

  3. #3
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    Thread Starter
    I thought the same thing, I didn't check amp draw on blower, but my fan is on high speed.

  4. #4
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    Keep on digging. The evap definitely does not have enough of a heat load.

  5. #5
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    Also make sure you don't have a suction line restriction upstream from where your gauge is connected.

  6. #6
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    Possible txv not opening enough?

  7. #7
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    Thread Starter
    The guys for your input, when I go back I will update on my findings. Tx again. Sometimes you just need an outsiders perspective

  8. #8
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    Quote Originally Posted by ksefan View Post
    Possible txv not opening enough?
    Looks like it. 30F SH.

  9. #9
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    Quote Originally Posted by ksefan View Post
    Possible txv not opening enough?
    The suction line is 58*. Txv may be closing- but it is effect, not cause.
    Txv is closing due to the low load.

    If txv was the sole issue, it would be starving the evap and the suction line would be up near IDB temp.

  10. #10
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    Quote Originally Posted by ksefan View Post
    Possible txv not opening enough?
    High superheat, high subcooling. Sounds like a restriction or TXV. Possibly LL screen before TXV clogged?

  11. #11
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    Quote Originally Posted by digitalinput View Post
    The suction line is 58*. Txv may be closing- but it is effect, not cause.
    Txv is closing due to the low load.

    If txv was the sole issue, it would be starving the evap and the suction line would be up near IDB temp.
    Always the chance of multiple issues. However 30 degrees superheat is an awful lot for a non adjustable TXV which most of these are. On a low air flow situation I would expect to see the superheat very low not high. Also OP, where are you taking the superheat reading, after the coil, or by the condensing unit? How long did it run? How long a line set?

  12. #12
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    Quote Originally Posted by icy78 View Post
    Always the chance of multiple issues. However 30 degrees superheat is an awful lot for a non adjustable TXV which most of these are. On a low air flow situation I would expect to see the superheat very low not high. Also OP, where are you taking the superheat reading, after the coil, or by the condensing unit? How long did it run? How long a line set?
    The SH is not as low as expected because the txv is doing its job- to open and close based on load.

    I bet if the OP takes the bulb off, the flood gates will open.

  13. Likes jmac00 liked this post.
  14. #13
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    Quote Originally Posted by digitalinput View Post
    The SH is not as low as expected because the txv is doing its job- to open and close based on load.
    In my experience I have found that the expansion valve controls to its set superheat . So if the air flow was low it would be struggling to maintain it's factory setting of 8 to 12 and we would probably see closer to 8 . The TX can't arbitrarily decide that because air flow is low it can increase its superheat.

  15. Likes Blake79 liked this post.
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