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Thread: subcooling

  1. #1
    I know how to determine required superheat but how do you determine what the required subcooling should be on a txv system

  2. #2
    Join Date
    Aug 2001
    residential system see the charging chart on the condenser

  3. #3
    Join Date
    Mar 2002
    Richmond, Virginia
    Page 3 of Jim Wheeler's tutorial is a good starting point.
    There is nothing more frightful than ignorance in action....Mark Twain

  4. #4
    I know how to check and adjust subcooling but dont know how to determine required subcooling. I have seen some carriers and on the name plate at the condensor it says txv subcooling. But on a trane it doesnt give a required subcooling,so how do I determine what the required subcooling should be on a trane. I would use the charging chart that came with the unit but lets say thats missing. THX

  5. #5
    Join Date
    Jan 2004
    I call Trane Technical Services, give my customer number and they give me technical data.
    Licensing laws are tough, and it's about time.

  6. #6
    Originally posted by mam123
    I call Trane Technical Services, give my customer number and they give me technical data.
    That works... what's your customer number?

    Oh well, I guess I just use mine for the time being...LOL

  7. #7
    10 degrees is minimum. residential systems will depend on seer rating and or heat pump or not. i charge till i get 10 degrees, then watch superheat. residential unit will come with an axv and not a txv normally. and i usually see around 22 degrees superheat. so best bet would be get subcooling to 10 then if superheat is higher than 25 degrees add freon till it comes down to 25. not exceading
    (cant spell it) 15 degrees subcooling.

  8. #8
    Join Date
    Apr 2004
    Subcooling is used to make certain that you do not have flash gas at the metering devise. Provided your liquid line is proper there is stall a pressure drop. In some cases a liquid line may see as much as 25psi drop. Now we dont see this since we dont generally have a tap at the liquid line near the indoor unit. The liquid line generally doesnt change sensible temperature from on end to the other by more than a degree.

    So if we have say a 240 psig liquid pressure (saturation temp about 115) and the line is 105 degrees. We have 10 degrees subcooling. Well, what is 105 degrees at saturation temperature? 211 psig roughly. So if at the liquid line near the evaporator is 211 or higher you will still have a solid column of liquid. In this case that covers the 25 psig pressure drop.

    For longer lines you may need to increase the subcooling to overcome the additional pressure drop.

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