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Old 12-05-2012, 09:45 PM   #1
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Can I charge via subcooling in the winter? (heat pump/txv)


I am reading up on how to check the charge on my r410a heat pump. Since it has a TXV I know that I need to use subcooling, but what I am unsure of is if I can do this when it is cold outside. The unit is a Goodman GSZ13024 and according to the product specs it should have 9 degrees +-3 of subcooling in COOLING mode. It doesn't specify subcooling in heating mode.

Can I check it in heating mode? Or is the only way to evacuate and weigh it in?

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Old 12-05-2012, 10:14 PM   #2
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Can I charge via subcooling in the winter? (heat pump/txv)


Call for cooling and charge for subcooling....It's easy to do subcooling in cooling.

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Old 12-06-2012, 05:31 AM   #3
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Can I charge via subcooling in the winter? (heat pump/txv)


Not sure anymore. But I think it has a piston in the outdoor unit for heating.
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Old 12-06-2012, 07:36 AM   #4
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Can I charge via subcooling in the winter? (heat pump/txv)


Without a subcool chart for heating you really wont know how much is right. Some brands with charts range from 5 to 25 in heating mode depending on coil matches. Your best bet is to measure air flow then charge to the correct BTU output.
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Old 12-06-2012, 10:33 AM   #5
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Can I charge via subcooling in the winter? (heat pump/txv)


weigh it in with an ACCURATE scale....if your in door coil is a true match and you calculated the line set length correctly then you you will be spot on.

One thing, Hvac5646 mentioned you have some splices of smaller diameter liquid line in the 3/8" copper?
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Old 12-06-2012, 11:55 AM   #6
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Can I charge via subcooling in the winter? (heat pump/txv)


Quote:
Originally Posted by Marty S. View Post
Without a subcool chart for heating you really wont know how much is right. Some brands with charts range from 5 to 25 in heating mode depending on coil matches. Your best bet is to measure air flow then charge to the correct BTU output.
Where can I find a subcool chart for heating? I don't have the tools or know-how to measure air flow or BTU output, but I have been meaning to learn about airflow so I will look into that.

Quote:
Originally Posted by hvaclover View Post
weigh it in with an ACCURATE scale....if your in door coil is a true match and you calculated the line set length correctly then you you will be spot on.

One thing, Hvac5646 mentioned you have some splices of smaller diameter liquid line in the 3/8" copper?
I do have 5/16" liquid line, with 3/8" spliced to the ends of it. I didn't notice this until after I installed my system because it was several feet out. One problem is that I do not have an accurate scale. I could certainly convert the LL to an equivalent 3/8" length based on volume, but then wouldn't I need to take into account the longer suction length somehow as well, or is it negligible since it is vapor?

I think my charge is pretty close, but I'd like to check it anyway if for no other reason than to learn something. This is the unit I have, for reference: split system.

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