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  1. #1
    Join Date
    Aug 2010
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    Goodlettsville,Tennessee
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    Is subcooling the best way to charge 410a?

    Finally came across 410a in the field. Is subcooling the only/best method for charging?I know I can't follow the 30 over ambient rule as with 22. Any simple rules to follow?

  2. #2
    Join Date
    Nov 2004
    Location
    Austin, TX
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    877
    There is no one best way with any refrigerant.

    I see a lot of 410 systems, my employer has been installing them since the late 90's and has a lot of 410 customers.

    As far as I know, the 30 over rule was fine for many older systems. My recent observations have seen the systems with relatively large condenser coils may only be 15 to 20 over if you were to check after getting everything right. In the last four years I've seen many Bryant/Carrier/Lennox systems with a 15 -20 degree over OAT high side P/T.

    Don't think pressure, think temps. It's not 70 psi, it's 40 degrees. It's not 118psi, it's 40 degrees.
    Many newer systems run a higher evap coil temp. Think 42-48 degrees, R22 or R410. Bryant/Carrier 410a systems with a TXV have a subcooling of 8 to 16. Check the data plate or the table inside the cover for the subcooling for the specific model/tonnage.

    Make sure airflow is right, charge fixed orifice by superheat, TXV by subcooling.

    After getting the subcooling right you can check the superheat to make sure the TXV is working. If the low side pressure looks way low then check the fan speed again. I've seen Bryant/Carrier equipment drop the furnace speed to the fan setting if not getting a signal on G and getting a Y signal (it's how some systems signal to dehumidify)(And the install crews kept on adding refrigerant to get the pressure up, never checking the airflow). On the VS systems dropping the G signal may half the CFM airflow.
    Thus part of checking for proper airflow is making sure you're getting a signal on G and any dip switches or motor taps are set for the CFM appropriate for the tonnage.

    On the ECM multi speed motors like they are using on some of the Lennox systems you still have to check the fan speed data and the system static pressure to make sure you have selected the proper speed tap. The ECM multi speeds doesn't maintain a set CFM like the VS motors do.

    Set airflow, charge by superheat for fixed orifice, charge by subcooling for TXV then check superheat.

    BTW, the biggest problem with 410a is the POE lubricant. It really soaks up the moisture and makes a molecular bond with it. It's also an excellent cleaner of crud from the inside of refrigerant lines. Thus techs who've never seen the need to flow nitrogen while brazing are getting a lot of plugged TXV's, screens or filters from the cupric oxide. The clogs may show up months later after install. As a service tech I get stuck with the issues. I flow nitrogen when I braze. I'm going to pressure test to 300psi with nitrogen anyway so it's not a big deal.

    You asked for simple.
    “I am for doing good to the poor, but...I think the best way of doing good to the poor, is not making them easy in poverty, but leading or driving them out of it. I observed...that the more public provisions were made for the poor, the less they provided for themselves, and of course became poorer. And, on the contrary, the less was done for them, the more they did for themselves, and became richer.”
    ― Benjamin Franklin

  3. #3
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    DIY
    I am an experienced, caring, trusted, service provider who solves my customers issues beyond there expectations by educating them and guiding them with value-building options to make excellent buying decisions while building security and wealth for my company, myself and my family.

  4. #4
    Join Date
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    Quote Originally Posted by Oldschoolmetal View Post
    DIY
    Yep.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

    RSES CMS, HVAC Electrical Specialist

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  5. #5
    Join Date
    Jun 2009
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    Bakersfield, Ca
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    Quote Originally Posted by timebuilder View Post
    Yep.
    I was told that weighing it in was the best way with appropriate lineset sizes and length. probably another myth.

  6. #6
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    Quote Originally Posted by Oldschoolmetal View Post
    DIY
    I think that is about the best way you can say it now on this site without getting into trouble Good call!

  7. #7
    Join Date
    Sep 2002
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    Finally came across 410a in the field. Is subcooling the only/best method for charging?I know I can't follow the 30 over ambient rule as with 22. Any simple rules to follow?
    That would depend on the type of metering device.

    If you work in the field, please through that silly 30 over ambient rule in the garbage even for R-22 systems. (A "pro" should know better) Easy rules of thumb shouldn't be necessary for anyone who understands the refrigeration cycle.
    General public's attitude towards our energy predicament: "I reject the reality of finite resource depletion and substitute it with my own; energy is infinite, we just need an alternative storage medium to run the cars on. The economy can grow indefinitely - we just need to "green" everything! Technology is energy! Peak what?"

  8. #8
    Join Date
    Jan 2004
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    Lancaster PA
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    As with R22, or any other refrigerant for that matter. Checking SH and SC is the best method. Even if you weigh the charge in. You should still check SH and SC.

    What method would you use to check the charge on a glass tender if it was R502, and used a cap tube metering device.

    What method would you use on a walk in freezer that used R502 and a TXV.

    What method do you use for a reach in cooler that uses R134A and has a cap tube metering device.

    Get your post count up to 15 and apply for pro membership. Once accepted, you'll have access tot eh pro forums, where there is lots of info on charging, and diagnosing equipment.
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  9. #9
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    Quote Originally Posted by beenthere View Post
    As with R22, or any other refrigerant for that matter. Checking SH and SC is the best method. Even if you weigh the charge in. You should still check SH and SC.

    What method would you use to check the charge on a glass tender if it was R502, and used a cap tube metering device.

    What method would you use on a walk in freezer that used R502 and a TXV.

    What method do you use for a reach in cooler that uses R134A and has a cap tube metering device.

    Get your post count up to 15 and apply for pro membership. Once accepted, you'll have access tot eh pro forums, where there is lots of info on charging, and diagnosing equipment.
    Understood. Especially with all the crappy components installed nowadays.

  10. #10
    Join Date
    Aug 2010
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    Swamp land
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    Why didn’t anyone say to charge R410 with liquid only? The real question is why was it not known to use Superheat for fixed restrictor systems and Subcooling for TXV systems. Is it know the basic idea to charging is to fill the evaporator with liquid refrigerant to a point without any of that liquid refrigerant getting back to the compressor?

  11. #11
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    Jan 2004
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    Lancaster PA
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    We aren't talking about a freezer. So you don't fill the evap.
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  12. #12
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    Aug 2010
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    Swamp land
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    I guess that was too vague. The idea to charging is to have the desired cooling affect the evaporator needs to have the right amount of refrigerant in it, be it liquid or liquid flashing to gas.

  13. #13
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    That is what we call superheat.
    I am an experienced, caring, trusted, service provider who solves my customers issues beyond there expectations by educating them and guiding them with value-building options to make excellent buying decisions while building security and wealth for my company, myself and my family.

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