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Thread: system recharge

  1. #51
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    Re: system recharge



    Actually, it is on topic, but not the best way to charge a system.

    Let's imagine that you are charging a TXV system. Further imagine that the service tech who worked on the system before you adjusted the TXV wide open. By the time you get the subcooling up, the compressor will be full of liquid and the system will be grossly overcharged.

    Or worse yet, if the compressor valves are broken, you are not going to get the subcooling up and you are not going to clear the sight glass, no matter how much refrigerant you dump into the system.

    You would have found these problems if you monitored the superheat as well as the subcooling.

    On a cap tube system, if you are just monitoring the superheat, you will miss restrictions and non-condensibles, as well as inefficient compressor.

    It pays to monitor both subcooling and superheat on both TXV and fixed orifice systems.

    Note: It is usually much easier to monitor the superheat at the compressor inlet rather than the evaporator outlet and serves the purpose.
    Last edited by Gary; 06-12-2008 at 08:39 PM.



  2. #52
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    Re: system recharge

    Here is a little story that may be slightly off topic, or perhaps not:

    I was inspecting a rooftop A/C system, which had 4 cap tubes.

    The superheat was within specs, but the subcooling was 38F/21K.

    I cut the cap tube assembly open to find that one of the cap tubes was brazed shut at its inlet.

    This was a factory braze.

    This unit was 18 years old and had been inspected every three months since new.

    That's 72 inspections by a wide variety of service techs and nobody noticed the problem.

    It pays to check subcooling as well as superheat.
    Last edited by Gary; 06-12-2008 at 09:01 PM.

  3. #53
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    Re: system recharge

    How do we charge an empty 2 stage cascade system?

    Do we charge both High Stage and Low Stage at the same time or

    Charge High Stage to reach a correct superheat/subcool or based on manufacturer specs the only proceed to Low Stage to a correct superheat/subcool or maufacturers specs?

  4. #54
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    Re: system recharge

    Sorry.. there is a typo error on the spelling.. so here it goes again..

    How do we charge an empty 2 stage cascade system?

    Do we charge both High Stage and Low Stage at the same time or

    Charge High Stage to reach a correct superheat/sub cool or based on manufacturer specs then only proceed to Low Stage to a correct superheat/sub cool or manufacturers specs?

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