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  1. #1
    Join Date
    Aug 2002
    Location
    Greenville SC
    Posts
    431
    I don't have the pleasure of working on Heat Pumps very often, so I thought I would ask the experts. I saw in this Forum one time an easy way to check the charge on a Heat Pump in the heating mode. It wouldn't give you the correct charge but would get you close, and close is all I need right now.

  2. #2
    What almost always works: the sight glass! If there isn't one, there are clamp on sensors that work almost like a sight glass.

  3. #3
    Join Date
    Nov 2000
    Location
    Lancaster, Pennsylvania
    Posts
    884

    Heat pump charge............

    Always the best route is to pull out all refrigerant from the system, find your multiplier and weigh it back in. Then you are 100% sure. I thought I read a few years back that you can take the outdoor temperature, add 126 to that # and your discharge line coming off the compressor should be roughly the same. I could be totally off on that one and today's higher efficiency equip. may blow that formula out of the water. Just keep in mind that a system that is over/undercharged is not good equipment longevity.
    KX500......the original big green meanie

  4. #4
    Join Date
    Jan 2006
    Location
    muncie Indiana
    Posts
    510
    actually no,
    You are right, check the oda and add 126 degrees to it this should be the discharge temp of the compressor. Not the liquid line but the actuall discharge tib off of the compressor. It is great. It's always a good idea to go back in the cooling season to double check it though. This can also be off if not a matched system.

  5. #5
    Join Date
    Nov 2006
    Location
    Gloucester Virginia
    Posts
    20

    Hmm

    Use the charging chart if its available and the system matches
    heattech

    If it hasnt worked properly since you serviced it last then why did it take the customer 2 years to complain??

  6. #6
    Join Date
    Aug 2002
    Location
    Greenville SC
    Posts
    431
    Thanks for the replys. The discharge temp is the quick meathod I thought I had read some where. Had a friend ask me to look at his unit, split system, no charts, fixed metering device, thus no sight glass.

  7. #7
    Join Date
    Apr 2004
    Posts
    7,680
    Originally posted by chilbrig
    I don't have the pleasure of working on Heat Pumps very often, so I thought I would ask the experts. I saw in this Forum one time an easy way to check the charge on a Heat Pump in the heating mode. It wouldn't give you the correct charge but would get you close, and close is all I need right now.
    Why not do it right? Close may work in heating but not cooling. Defrost is cooling so "close" may leave you with poor efficiency, poor defrost, and worse.

    You can use one of many methods for checking the charge but when it comes down to adjusting the charge you should follow the charging procedures by that manufacturer. That 126 will not work on every thing.

  8. #8
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    The 126 above ambient method is a procedure Goodman specified for thier heat pumps. It will usually get you very close with any heat pump that uses a fixed orifice for metering in the outdoor unit.

    It doesn't work all that well on heat pumps that use a TXV in the outdoor unit though. Since the TXV is controlling the superheat to the compressor, the discharge superheat will also be stable, resulting in a more stable discharge temperature. Depending on the setting of the TXV and ambient conditions, the heat pump may run a significantly cooler or warmer discharge line when correctly charged than a fixed metered heat pump would.

    Trane uses TXVs in all of thier heat pump outdoor units, but the provide performance charts that tell you what the pressures should be based on the indoor and outdoor temperatures and the indoor unit the heat pump is matched with. The graph itself is for a specific indoor unit/coil, if the system has a different Trane indoor unit/coil, there is a list of matching indoor units/coils that tell gives correction factors to the chart for that matchup.

    [Edited by mark beiser on 11-21-2006 at 12:43 PM]
    If more government is the answer, then it's a really stupid question.

  9. #9
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681

    Definately follow manufacturer procedures

    usually fixed bore systems have critical charges, so trying to get close could cause heartaches down the road -- follow the manufacturers procedures.

    Some techs use the touch test to get temperature differences across the reversing valve to get a feel for how close a charge is.

    Originally posted by docholiday
    Originally posted by chilbrig
    I don't have the pleasure of working on Heat Pumps very often, so I thought I would ask the experts. I saw in this Forum one time an easy way to check the charge on a Heat Pump in the heating mode. It wouldn't give you the correct charge but would get you close, and close is all I need right now.
    Why not do it right? Close may work in heating but not cooling. Defrost is cooling so "close" may leave you with poor efficiency, poor defrost, and worse.

    You can use one of many methods for checking the charge but when it comes down to adjusting the charge you should follow the charging procedures by that manufacturer. That 126 will not work on every thing.

  10. #10
    Join Date
    Sep 2001
    Location
    Vancouver Canada
    Posts
    996
    It's just a ***** to charge heatpumps in heat mode. If you have a matching system best way unfortunatly is to pull the charge and weigh it back in, if it is not a match then maybe go with the 126 plus ambient and that should put it reasonably close. Best to wait for warmer weather and check it again in cool mode. I hate having to go back but that is the best solution I have found.
    "Go big or Go Home"

  11. #11
    Join Date
    Feb 2004
    Posts
    2,597
    a "touch test" is useless.

    126 over ambient is goodman only.

    follow the manufacturers charts.

  12. #12
    Join Date
    Oct 2006
    Location
    Emerald Coast, FL 30.1N 85.8W
    Posts
    681
    It's not useless if you know what your doing. Doing a touch test on the suction, discharge, and reversing valve saves a lot of time.

    I own 8 units, two of which are heat pumps. I can tell system performance by touch without attaching gages or temp probes.

    Originally posted by billva
    a "touch test" is useless.

    126 over ambient is goodman only.

    follow the manufacturers charts.

  13. #13
    Join Date
    Aug 2004
    Location
    North Richland Hills, Texas
    Posts
    14,914
    Originally posted by emcoasthvacr
    usually fixed bore systems have critical charges, so trying to get close could cause heartaches down the road -- follow the manufacturers procedures.

    Some techs use the touch test to get temperature differences across the reversing valve to get a feel for how close a charge is.
    We don't call those "techs" around here, we have other names for them.

    You do realize that your statements are contradictory don't you?

    Originally posted by emcoasthvacr
    It's not useless if you know what your doing. Doing a touch test on the suction, discharge, and reversing valve saves a lot of time.

    I own 8 units, two of which are heat pumps. I can tell system performance by touch without attaching gages or temp probes.
    Please enlighten us oh master of the beer can method, Other than just a very general impression of how the system is running, what can you tell about the performance of a system by feeling the pipes?
    If more government is the answer, then it's a really stupid question.

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