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Thread: High Head, High Sc on 410 Split System

  1. #1
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    High Head, High Sc on 410 Split System

    It's cooling, but obviously well off spec. Txv replaced 3 months ago, performed well up to now. Charge weighed in 3 months ago. Consenser coil thoroughly cleaned today.

    Here are the numbers at 88 outside and 77 indoors:
    400/144
    Sc 25
    Sh 7
    Suction temp 57
    Liquid line temp 93
    Lsat 118
    DeltaT, a lousy 8 degrees

    Condenser fan output seems normal.

    Ideas.

  2. #2
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    System is overcharged ?
    Check for leaky returned air.
    Where's the indoor unit located ? Attic ?

  3. #3
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    Thread Starter
    Air handler in attic, no air leaks, I realize overcharge is #1 suspect, but pretty confident that the charge weighed in correctly.

    Could be a restriction, or a problem with the fairly new txv. This unit has txv's at the evaporator and also at the condenser.

    Could warm the sensing bulb in attic and see what pressures do.

    Could recover 1/2 lb and see where sc goes.

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  5. #4
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    Thread Starter
    Recover 1/2 lb, sound like a good idea?

  6. #5
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    Thread Starter
    Recovered 1 lb of R410a from 2 ton system.

    New readings, but OS temp about 4 degrees cooler.

    380 head, down about 15
    Suct 139, unchanged
    Sc. 21​ ​ to 23, down about 4
    Sh 9- 11, up about 3
    Suc temp 58-59, up about 2
    Llt 92, same
    Lsat 113, down 5
    Delta t, still 8

  7. #6
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    Are these symptoms of Heat Strips turning on somehow ?

    I've never seen it myself .... well .... not in the summer ... I saw one stuck in the winter because the fan board relay
    Tell your Cat I said "Psst Psst Psst"

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  9. #7
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    High Head, High Sc on 410 Split System

    Quote Originally Posted by Snapperhead View Post
    Are these symptoms of Heat Strips turning on somehow ?

    I've never seen it myself .... well .... not in the summer ... I saw one stuck in the winter because the fan board relay
    Welded contactor, possibly, but I’ve also seen it where a T6 stat was installed and emergency heat is tied to W and not AUX/E on the thermostat. For some reason W feeds just enough voltage constantly when the stat is programmed for heat pump operation.

    Few things to check, but I figure someone would probably notice if it’s been 3 months since install.

    Edit: Just read only TXV replaced, unless thermostat was recently installed disregard most of this. My mistake.


    Sent from my iPhone using Tapatalk

  10. #8
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    Quote Originally Posted by etbrownx View Post
    Recovered 1 lb of R410a from 2 ton system.

    New readings, but OS temp about 4 degrees cooler.

    380 head, down about 15
    Suct 139, unchanged
    Sc. 21​ ​ to 23, down about 4
    Sh 9- 11, up about 3
    Suc temp 58-59, up about 2
    Llt 92, same
    Lsat 113, down 5
    Delta t, still 8
    .
    Still overcharged, a good chance it's oil logged...do you have an IR camera or visual or evap?
    ..
    Do not attempt vast projects with
    half vast experience and ideas.
    ...

  11. #9
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    No mention of airflow. Static pressure, return and supply wb/db.

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  13. #10
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    The pressures are off but not enough to cause an 8° TD so I suspect you're picking up heat somewhere.
    I don't know what type of system you have but you could just pull the disconnect to the outside unit during a call for cooling & check the supply temp.
    That's one way to see if you're picking up heat from the blower unit.
    Gary
    -----------
    http://www.oceanhvac.com
    The best things in life are free but not everyone is willing to pay the price.

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  15. #11
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    " The pressures are off but not enough to cause an 8° TD so I suspect you're picking up heat somewhere."
    +1

  16. #12
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    Thread Starter
    Gary's idea is worth a try. Fyi, Unit is producing plenty of condensate as well.

    Alternate idea would be to read the amps on the air handler in cool mode.

  17. #13
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    24 hrs after removing some refrigerant, it's getting strange. DeltaT is now 14, and we changed nothing. Daily outside temp about the same as before. 14 is obviously still sub par.

    I figured maybe a possible obstruction in the lines or coils cleared itself. Maybe.

    A very sharp tech buddy says he's seen cases with R410a where adjusting a charge can take 24 hrs for the txv to adjust.???

    Never heard of such. For example, replace a compressor, drop the 410a charge and typically in 15 minutes you have stable pressures.

    Anybody heard of 24 hrs for a txv to adjust?
    Last edited by etbrownx; 08-08-2022 at 02:12 AM. Reason: Clarity

  18. #14
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    No

  19. #15
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    Quote Originally Posted by VTP99 View Post
    No
    Ditto
    Valve mfg instructions list up to 15 minutes.

  20. #16
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    Quote Originally Posted by etbrownx View Post
    24 hrs after removing some refrigerant, it's getting strange. DeltaT is now 14, and we changed nothing. Daily outside temp about the same as before. 14 is obviously still sub par.

    I figured maybe a possible obstruction in the lines or coils cleared itself. Maybe.

    A very sharp tech buddy says he's seen cases with R410a where adjusting a charge can take 24 hrs for the txv to adjust.???

    Never heard of such. For example, replace a compressor, drop the 410a charge and typically in 15 minutes you have stable pressures.

    Anybody heard of 24 hrs for a txv to adjust?
    Sometimes Oil gets in the wrong places and it takes a while to get back to the compressor where it belongs .... and I think it acts as a restriction
    Tell your Cat I said "Psst Psst Psst"

  21. #17
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    Last week I worked on a 27 yr old Bryant 2.5 ton HP

    Found the air filter 80 percent clogged solid because someone built the trap in front of the access flap

    After about 15 minutes my SH was hanging at 30 , SC 20

    Im like .... dam ... your TXV shut down .... let me order one

    Couple days later hes like "dude its been 70 deg inside and its 95 outside"

    I havent went back yet because ive been stupid busy .... but Im guessing "oil" was messing with it
    Tell your Cat I said "Psst Psst Psst"

  22. #18
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    You had low air flow, low suction saturated, potential moisture icing at txv inlet/screen.

    Correct air flow, higher suction saturated, no icing restriction.

    Running at full load, normal conditions will return oil rapidly. Excess oil will affect discharge sh and be apparent.

  23. #19
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    Amp draw to air handler will rule out electric heat stuck on. I had one the other day with a back feed through fan relay board energizing heat relay . It may sound too simple but have you tried to clean condenser coil. You know when you start hosing it out

  24. #20
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    Bro! Me too. I had a restriction on a Bryant packaged unit. Screaming compressor, high head etc. I come back with a new txv the next morning and the Shit is purring. Didn’t understand that one til this day

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