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  1. #1
    Join Date
    Jan 2011
    Location
    Maryland
    Posts
    9

    Low Subcooling Low Superheat?

    I am working on a two stage heat pump with a varable speed air handler.
    The system runs about 1.5 deg S/C and about 2 deg S/H The delta T is 22 deg. A capacity check shows systems is operation at 122% of publish Capacity. Adding refregerant does not change the S/C much at all.
    My question is how is this possable? low subcooling and low S/H
    This is a matched system, and all test equiment was checked for accuarcy.

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,970

  3. #3
    Join Date
    Jun 2004
    Posts
    847
    Is the compressor and evap motor at 100% ?
    What kind of airflow to your air handler?

  4. #4
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,970
    You've got multiple problems, I think.

    Please provide all of the readings that you took on the unit along with model and serial and maybe we can see a problem.

  5. #5
    Join Date
    Jan 2011
    Location
    Maryland
    Posts
    9
    25HNB624 with an FE4ANF003 Air Handler.
    90 deg ODBD Pressures 298/138# liquid line@ service valve 93deg vapor @ service valve 52 deg.
    air flow @ 700 CFM +/- 20 cfm
    RA 76 deg db 67 Deg wb
    SA 54 deg db 52 Deg wb

  6. #6
    Join Date
    Jan 2011
    Location
    Maryland
    Posts
    9
    Compressor @ 60% of fla air flow @ 700cfm

  7. #7
    Join Date
    Jul 2004
    Location
    Massachusetts
    Posts
    6,826
    You may have a flooded everything due to a gross overcharge. Start by recovering all the refrigerant from the system. The start with a fresh charge to factory specs and see where things are at that point.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  8. #8
    Join Date
    Jan 2011
    Location
    Maryland
    Posts
    9
    The Refrigerant charge was recovred and weight back in @ factory specs added 5 lbs more. and removed 10lbs. still little change is s/c

  9. #9
    Join Date
    Nov 2006
    Location
    Southeastern Pa
    Posts
    17,012
    Quote Originally Posted by MIDCAM View Post
    The Refrigerant charge was recovred and weight back in @ factory specs added 5 lbs more. and removed 10lbs. still little change is s/c

    I would have loaded just the factory spec amount and continued the diag from there. No need to add 5 more lbs....
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  10. #10
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,970
    Where, exactly, are you measuring the liquid line pressure and temperature?

    Where, in relationship to the liquid drier?

  11. #11
    Join Date
    May 2007
    Location
    Central NJ Area
    Posts
    779
    I'm guessing it's metered by a txv? Could the txv be causing the issue?

  12. #12
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    24,970
    Quote Originally Posted by MIDCAM View Post
    The Refrigerant charge was recovred and weight back in @ factory specs added 5 lbs more. and removed 10lbs. still little change is s/c
    No offense, but a part of me is questioning your instruments.

    I just can't see adding 5 pounds of refrigerant without affecting subcooling unless you have an extraordinarily long lineset.

  13. #13
    Join Date
    Jan 2011
    Location
    Maryland
    Posts
    9
    As did I with three different instruments A cooper digital. Field Piece digital. And my old standby yellow jacket and fluke temperature probes. Nothing makes sense. How can a evap show flooded and the condenser be starved?

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