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  1. #1

    HP Charged in Winter -- Check Subcooling in Spring?

    Just had a newer R-410A Heat Pump repaired during winter weather conditions and the tech had to evacuate the lineset. He deep vacuumed down to the 500 micron level then re-charged the system.

    Since it was too cold outside, he was unable to verify charge using Subcooling Method. Unsure of the exact lineset length, he added refrigerant and then followed the Heat Pump Charging chart to check the lineset pressures vs. indoor & outdoor temps.

    Without weighing the charge, I guess this got him pretty close and within the tolerances of the relationship chart. Since this system uses a TXV @ indoor coil, I thought the subcooling method (with superheat verification) is the most accurate way to check charge. I just want to make sure the charge is exactly right.. I know a few ounces in either direction can make a significant difference on these new high-efficiency units. I've noticed some horizontal frost bands on the outside coil at 35-40 degrees OAT that didn't happen before.

    Should I call them back in the spring-late summer and request a proper subcooling check be performed or did he get it right using the heating mode chart??

    THANKS!!

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    68,064
    Indoor TXV is bypassed in heating mode.
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  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
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    We go back in the spring to recheck things. It is more accurate to check in cooling mode on a warm day.

  4. #4
    Join Date
    Nov 2009
    Location
    north georgia
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    19
    Did he weight the charge specified on the rating plate and then add more, or did he just add refrigerant till the pressure was good according to the chart?

  5. #5
    Join Date
    Sep 2002
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    Northeast Ohio
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    4,842
    Quote Originally Posted by Gaskeeter View Post
    Did he weight the charge specified on the rating plate and then add more, or did he just add refrigerant till the pressure was good according to the chart?
    OP wrote........


    Quote Originally Posted by RockRiver View Post
    Without weighing the charge, I guess this got him pretty close and within the tolerances of the relationship chart. Since this system uses a TXV @ indoor coil, I thought the subcooling method (with superheat verification) is the most accurate way to check charge.
    A good HVAC tech knows how, an educated HVAC tech knows why!

    DEM


  6. #6
    Did not weigh the charge because lineset length was unknown. Didn't see him use a scale or anything. Whole system was not evacuated, just the lineset.

    He throttled in liquid through the suction side a few times and then said the pressure/temps matched according to the manufacturer's heating chart.

    I have been noticing the coils frosting more quickly and the whole outdoor unit froze over in about 45 mins when the OAT was only about 33-35*. Coil was entirely frozen so no airflow -- the outdoor unit fan would try to spin, but couldn't. Defrost melts it off, but defrosts are talking longer... Full 10min cycles and still not reaching termination temp of 65 (after the 10 min max time, it gets to upper 50's, but won't terminate sooner like it should if it can reach 65). I guess I could change the jumper to 30 min defrosts from 60 min, but that just seems too frequent and not efficient.


    Any ideas?

  7. #7
    Join Date
    Nov 2009
    Location
    north georgia
    Posts
    19
    Don't change the jumper,sound's like the pressure is still off a bit. You might give them a call and tell them how your system is doing.

  8. #8
    Join Date
    Jan 2010
    Location
    North Huntingdon,Pa
    Posts
    356
    on a non adjustable txv- it should be charged to mfg's subcooling specs in cooling mode-the superheat is what it is at designed subcooling

  9. #9
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,158
    In a cooler climate with timer defrost, I'd shoot for no more than 60 minutes. Many around here are left on 90 minutes, like the one down the street. That poor sucker spends a lot of the winter heavily frosted.

  10. #10
    Join Date
    Dec 2009
    Posts
    53
    what is your delta T between supply and return? sounds like you need to get your service tech back out.

  11. #11
    Join Date
    Aug 2011
    Posts
    1,199
    what is acceptble delta t temp in heatrpump heatmode?is 20 f or more is good?and what is liquid line(bigger line) temp should be in heatmode?i read some post is 110 plus ambient temp?is that right?linetemp too low remove charge,to high add charge?

  12. #12
    Join Date
    Jan 2010
    Location
    North Huntingdon,Pa
    Posts
    356

    ?

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    +110 ,that was goodman's old way of charging, they now want it weighed
    PA#9377
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