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Thread: This on has me baffled

  1. #1
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    This on has me baffled

    Replaced TXV about a month ago. Got called back and system iced up/low cool.

    Here are my numbers...
    Return Air-72°
    Supply Air- 54°

    Suction
    140# 66°

    Liquid Line
    325# 77°

    Outdoor Ambient-80°

    What am I missing? I may just be over tired, but just don't see how this could be.

    Any help appreciated.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  2. #2
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    Is the old TXV there? If so, how does the strainer look? Maybe there’s junk in the system and clogged your new TXV. Definitely looks like a restriction, but your temperature split looks weirdly alright, depending on your return wet bulb.

  3. #3
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    Are those temps next to suction and liquid reading the suction and liquid line temps? Looks like you have very high sub-cooling if that's the case.

    Might be a failing compressor if I understood your readings correctly.

  4. #4
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    Indoor fan cutting out intermittently???

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  5. #5
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    Quote Originally Posted by CircusEnvy View Post
    Is the old TXV there? If so, how does the strainer look? Maybe there’s junk in the system and clogged your new TXV. Definitely looks like a restriction, but your temperature split looks weirdly alright, depending on your return wet bulb.
    Looks like a restriction to me, too. That is why I don't get the good Delts T. And with a 54 degree supply air, why is the suction line at the service valve at 66 degrees. The more I think about this the more confused I become.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  6. #6
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    How do you have 325 PSIG on the liquid line with a 77 degree line.I'm assuming this is R410A? At 325 PSIG you should have about a 100-105 degree liquid line.Is this R410A.Sounds like plugged drier, or plugged TEV screen.Whats your sub cooling and superheat.Sounds like your starving.Check to see if there is a big temp diff.across the drier.

  7. #7
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    Quote Originally Posted by joemach View Post
    Looks like a restriction to me, too. That is why I don't get the good Delts T. And with a 54 degree supply air, why is the suction line at the service valve at 66 degrees. The more I think about this the more confused I become.
    You could still have a good delta T if airflow is poor, but actual enthalpy change is probably low. That might also explain the freezing (low airflow + restriction). Return/supply wet bulb and CFM would help determine that.

  8. #8
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    This on has me baffled

    Hard to see how a system freezes up at #140 , especially with the space already down to 72 degrees. Someone screwing with the stat? Maybe an intermittent blower motor?


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  9. #9
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    Suction sh ~17*f maybe a little high
    Sub cooling ~ 15*f should be ok
    Suction temp is between return air & suction saturated temp, ok
    Condenser approach ~ 15*f , ok
    Liquid line approach ~ 3*f, ok
    Evap DT ~ 18*f, ok
    no return wb temp, supply air seems really close to suct sat.

    If the inside wb is high, check the external static for low air flow.

    Overall not to bad. I`d go along with 'newoldtech", intermittent blower issue (wiring, relay, brgs, capacitor, t'stat). Duct insulation loose, dirty filter (changed after calling you), someone blocked the return, had a plastic bag once in the return do crazy things on each cycle.

  10. #10
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    Quote Originally Posted by ehsx View Post
    Suction sh ~17*f maybe a little high
    Sub cooling ~ 15*f should be ok
    Suction temp is between return air & suction saturated temp, ok
    Condenser approach ~ 15*f , ok
    Liquid line approach ~ 3*f, ok
    Evap DT ~ 18*f, ok
    no return wb temp, supply air seems really close to suct sat.

    If the inside wb is high, check the external static for low air flow.

    Overall not to bad. I`d go along with 'newoldtech", intermittent blower issue (wiring, relay, brgs, capacitor, t'stat). Duct insulation loose, dirty filter (changed after calling you), someone blocked the return, had a plastic bag once in the return do crazy things on each cycle.
    Thanks ehsx for your insight. My major concern was the supply air temp vs. the suction line temp. Never saw that big a spread. First time for everything. Where is it picking up heat? Only a 15 foot lineset all wrapped up.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  11. #11
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    It is picking it up in the evaporator. 72*f return air is still above the suction temp. Check the air flow. Easiest way is with u-tube, total external static typically less than .5".

  12. #12
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    Restricted LLFD in the condenser cabinet.
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    How many times must one fix something before it is fixed?

  13. #13
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    Quote Originally Posted by beenthere View Post
    Restricted LLFD in the condenser cabinet.
    Now that is a definite possibility.

    Thanks
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  15. #14
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    If it is a restricted LLFD or a TXV then the suction press should be low. as compared to 140PSI.yes/no?

    Way back the ROT(rule of thumb was 72-52-32) 72* return air- 52*F air off of coil-32*F SST inside coil. You have 72-54-??. So your evap SST should be 36/38/40? How do you get 66*F at the CU?

  16. #15
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    Quote Originally Posted by TechmanTerry View Post
    If it is a restricted LLFD or a TXV then the suction press should be low. as compared to 140PSI.yes/no?

    Way back the ROT(rule of thumb was 72-52-32) 72* return air- 52*F air off of coil-32*F SST inside coil. You have 72-54-??. So your evap SST should be 36/38/40? How do you get 66*F at the CU?
    That is the mystery to me. I don't see how that could be. I don't see how that could be.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  17. #16
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    Quote Originally Posted by TechmanTerry View Post
    If it is a restricted LLFD or a TXV then the suction press should be low. as compared to 140PSI.yes/no?

    Way back the ROT(rule of thumb was 72-52-32) 72* return air- 52*F air off of coil-32*F SST inside coil. You have 72-54-??. So your evap SST should be 36/38/40? How do you get 66*F at the CU?
    Someone else may have added charge to get the vapor pressure up not realizing the LLFD was restricting.

    I've had TXVs feed enough to keep the lower rows of the evap cold, but the top rows were warm. So the cold refrigerant from the lower part of the coil kept the suction line cool/cold.
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  18. #17
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    Quote Originally Posted by ehsx View Post
    Suction sh ~17*f maybe a little high
    Sub cooling ~ 15*f should be ok
    Suction temp is between return air & suction saturated temp, ok
    Condenser approach ~ 15*f , ok
    Liquid line approach ~ 3*f, ok
    Evap DT ~ 18*f, ok
    no return wb temp, supply air seems really close to suct sat.

    If the inside wb is high, check the external static for low air flow.

    Overall not to bad. I`d go along with 'newoldtech", intermittent blower issue (wiring, relay, brgs, capacitor, t'stat). Duct insulation loose, dirty filter (changed after calling you), someone blocked the return, had a plastic bag once in the return do crazy things on each cycle.
    I see 24* subcool. Maybe I am wrong.

    Seems like refer stuck in condenser keeping it cooler.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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