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  1. #1
    Join Date
    May 2008
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    7

    confused with goodman 2ton

    I am a new residential service tech with limited experience. I just installed a new goodman 2ton system in my 1900 sqft home. It has a sealed envelope of spray foam insulation. It is very tight. I can't seem to get a split that is greater than 14-15 degrees. My line set is right at 50 ft, it is a 13 seer goodman, I can't seem to figure it out. I verified the .059 piston is what goodman recommends. My pressures are 85 suction and 210 liquid. I had 9-10 degrees superheat. It was 85 degrees outside with 66% Rh, and inside it was 75 degrees with a whopping 85% Rh. It does not seem like the unit is able to pull much moisture out of the air. It was able to bring the temp down to 70 degrees after a good, long run time, but the Rh didn't drop much, it was at 68%. I am not very experienced but it seem like to me the pistion might be too large,,,I think my suction pressure should be lower????? Could my problem be that the spray foam envelope is causing a very high Rh and the unit can't handle it??????? I do have 7 inch duct that was dampered off that is ran to the exterior. I can ask a more experience tech at work but since this is my own house I am gonna try and work through it. Any help will be greatly appreciated.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    67,910
    What was your CFM.
    What was your indoor wetbulb.
    You won't get a big split until the more of humidity is removed.
    Was split measured at coil, or at supply and return grilles.
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  3. #3
    Join Date
    Feb 2008
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    Guam
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    168
    2 ton unit in a 1900 sq ft home? better check your tonnage again or maybe a typo, most residental service techs I know would not have asked this question./shrug
    Also your humitidy is way high.
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  4. #4
    Join Date
    Jan 2005
    Location
    USA
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    1,450
    Quote Originally Posted by beenthere View Post
    What was your CFM.
    What was your indoor wetbulb.
    You won't get a big split until the more of humidity is removed.
    Was split measured at coil, or at supply and return grilles.
    Agreed and also 1900 square feet on 2 ton unit. I think you need to recalculate tonnage, use manual j to get closer I would of thought that it would be closer to 2.5 maybe 3 ton. My house is small 1500 and 2.5 ton for ohio high humidity 90+ at 90+ temp in summer and runs constantly to keep up on those days.
    "It's always controls"

  5. #5
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    Jan 2004
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    It may be borderline on its size.
    But an undesized A/C wouldn't have a high humidity after a long run to bring the temp dpwn to 70*F.

    Plus, spray foam insulated houses have a very low heat gain.
    That 7" dampered off intake, may not be closed enough.
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  6. #6
    Join Date
    Aug 2007
    Location
    MN
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    2,677
    I would question fan speed(cfm) and whether the charge is proper. my guess is blowers on high.
    You can't fix stupid

  7. #7
    Join Date
    Sep 2002
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    Quote Originally Posted by skwsproul View Post
    Agreed and also 1900 square feet on 2 ton unit. I think you need to recalculate tonnage, use manual j to get closer I would of thought that it would be closer to 2.5 maybe 3 ton. My house is small 1500 and 2.5 ton for ohio high humidity 90+ at 90+ temp in summer and runs constantly to keep up on those days.
    1 ton per 1000 sq ft. is common in mild climates. (At least in southern ontario it is)

  8. #8
    Join Date
    Apr 2008
    Location
    Alberta Canada
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    2,246

    Seems high

    Quote Originally Posted by amd View Post
    1 ton per 1000 sq ft. is common in mild climates. (At least in southern ontario it is)
    have a 2 ton in my 2200 sq' house it is alittle small, keeps us comfortable, but I have 2 furnaces and plan on putting another 1.5 to 2 ton unit this year just for speed. I think 800 sq' per ton is max. We do not have high humidity and I know you want longer cycles for proper humidity removal. I use f-280 load calculation.
    Do it right the first time.

  9. #9
    Join Date
    Jan 2005
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    USA
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    Quote Originally Posted by amd View Post
    1 ton per 1000 sq ft. is common in mild climates. (At least in southern ontario it is)
    Do you reach 90 there. Smaller unit may work on most days here but at 90+ the inside temp/humidity would be unbearable and I dont know about most techs but when I spend a day outside like that I expect my house to be almost too cold when I get home. Are the more efficient units more capable of handling a larger load? If so would there be humidity issues? Note that I do commercial and do not size units at all, i just go from my experience on that and could be wrong. If you know better please show me specnical stuff.
    "It's always controls"

  10. #10
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  11. #11
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    Jan 2004
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    Lancaster PA
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    Commercial and residential sizing are 2 very different things.

    High insulation values, low infiltration rate, shaded windows will lower required A/C size.
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  12. #12
    Join Date
    May 2008
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    7
    Yes, fan is on high speed. Manual J showed 2 ton to work, but a variable speed was suggested, this is not a variable speed. I'm guessing that if fan speed is changed to low or medium speed then it will pull more moisture frome air due, am I correct?

  13. #13
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    Yes, it will remove more moisture. It will also allow it to run longer to remove more moisture.

    If you did a room by room load calc, that load calc told you how many CFM to each room.
    That is what you would use in conjuntion with Manual D to determine fan speed setting.
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