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  1. #1
    Join Date
    May 2004
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    Just set up a new system in my own home. Goodman 13 seer 2.5 ton with txv. Set subcooling to 13 and compressor superheat to 20. High psi 210 low 75 at 90 deg mbient. Temp drop across coil is 19 deg. I understand if you run lower pressures the system should be more efficient. My question is how low can you go? System is now charged to Goodman specs but I noticed at lower pressures I can still get 18 or 19 deg drop across the coil. So should I throw the specs out the window and charge to the minimum pressure to still get proper coil temp? How low can I go with superheat and still keep the scroll compressor happy? I currently service units in an upper class housing complex where money is not an issue so I never gave much thought to efficiency. Unfortunately they don’t give me much of it so every penny counts. Thanks

  2. #2
    Join Date
    Oct 2003
    Florida's space coast
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    Stay within the specs if you want your system to have a long life.

    If thats not a priority run it under charged and replace the compressor every couple years.
    We've been doing so much,for so long,with so little, that now we can do almost anything, with nothing at all.

  3. #3
    Join Date
    Aug 2003
    Fort Worth, TX
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    You'll lose out big time under higher loads and higher ambients with an undercharge. Compressor will run hot and you'll kill your efficiency. TXV's are a little more forgiving to a small overcharge but don't do a great job when they don't receive a solid column of liquid from the liquid line. Starving an evap is never a good idea.

    If you set your system to "minimum pressures" on a mild day, you may find it laying over and flopping like a fish out of water on a really hot day.
    Building Physics Rule #1: Hot flows to cold.

    Building Physics Rule #2:
    Higher air pressure moves toward lower air pressure

    Building Physics Rule #3:
    Higher moisture concentration moves toward lower moisture concentration.

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