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Thread: Superheat

  1. #14
    Join Date
    Mar 2013
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    11
    Mfr specs are always a good start and in your situation Subcooling at the ODU for starters. Don't forget the air filter (apartments), and condition of your IDC and ODC. We sometimes get so fixed on pressures, we forget air flow.

    Respectfully,
    d

  2. #15
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    Jan 2013
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    Mistake by the lake
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    It is interesting to see the varying opinions on this subject. True superheat can only be taken at the evap exit by definition. The difference between saturation temp and evap exit temp. same for sub-cooling with condenser exit. In this case there is no way to know what the temp at the condenser should be without access to the evap exit line. I would also give the advice of calculating your target superheat and not worry about it. Most target superheat charts are +/-5 degrees anyway. As long as your split is ok for the humidity you'll be fine.

  3. #16
    Join Date
    Apr 2009
    Location
    British Columbia, Canada
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    38
    Charge by approach?

  4. #17
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    Feb 2013
    Location
    Lamar, SC
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    Don't forget that the purpose of superheat is to ensure all the refrigerant is in a vapor to eliminate flooding the compressor, so checking at the condensing unit is just fine since that is where the compressor is.
    "If you've eliminated all other possibilities whatever remains must be the truth."

  5. #18
    Join Date
    Feb 2009
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    Tallahassee, FL
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    Quote Originally Posted by jmsmars1 View Post
    Don't forget that the purpose of superheat is to ensure all the refrigerant is in a vapor to eliminate flooding the compressor, so checking at the condensing unit is just fine since that is where the compressor is.
    If you dont measure SH at evap and have significant heat gain in lineset ......its easy to overcharge to get target SH at outdoor. If unit is a heat pump this can cause issues.

  6. #19
    Join Date
    Jul 2006
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    1,091
    Quote Originally Posted by klee7013 View Post
    Disagree with ya there
    some places with poor armorflex and/or 50' lineset in a attic that is 130 F
    i do check on the outside and if it looks normal then i may not check coming out of the IDC. But if the SH seems high i prefer to go check it coming out of the coil so i can see what is going on with the system. JMO
    All the more reason to read superheat with in 6" of the compressor. The refrigerant is also used to keep the compressor cool/keep it (the compressor) from going out on high temp. Take it at the indoor coil you'll be under charged.

  7. #20
    Join Date
    Jan 2013
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    Mistake by the lake
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    Quote Originally Posted by rickboggs View Post
    All the more reason to read superheat with in 6" of the compressor. The refrigerant is also used to keep the compressor cool/keep it (the compressor) from going out on high temp. Take it at the indoor coil you'll be under charged.
    What if your lineset is picking up 10 degrees of heat and your target superheat is 10 degrees. You take the temp near the compressor and add accordingly. You just moved the saturation point in the evaporator to the outlet. No change of state=no BTU gain=no cooling=hot unhappy person. Who pays for that return call?
    Last edited by Itstartedasacc; 03-30-2013 at 12:24 AM. Reason: rewording

  8. #21
    Join Date
    Jun 2002
    Location
    Dacula, GA
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    12,637
    Quote Originally Posted by beenthere View Post
    So you have schrader fittings at the IDC of these units. Or you just guess what the pressure is at the IDC.
    Well been he could have all day to Service a unit and walk back & forth evap to cond don't you know. LOL



    R

  9. #22
    Join Date
    Jun 2004
    Posts
    863
    [QUOTE=Itstartedasacc;15482141]What if your lineset is picking up 10 degrees of heat and your target superheat is 10 degrees. You take the temp near the compressor and add accordingly. You just moved the saturation point in the evaporator to the outlet. No change of state=no BTU gain=no cooling=hot unhappy person. Who pays for that return

    No change of state does not mean no heat is absorbed
    Latent heat is absorbed.
    Unit will still cool as long as an acceptable evaporator TD is maintained.
    Even if saturation point is in the compressor.
    Compressor will not last long but will still cool.

  10. #23
    Join Date
    Dec 2012
    Location
    columbus, OH
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    2,042
    This is a great bebate. But, dont forget he doesnt have acess to do it the proper way. In my experience this is because LL did not get signatures. In this case, do your best and dont worry about it.

  11. #24
    Join Date
    Jul 2006
    Posts
    1,091
    I can have a 40 degree coil with a 25 degree super heat.... add refrigerant..... then have a 40 degree coil and 15 degree super heat.... all measured between the accumulator and compressor. This pdf is for old Rheem units with fixed metering. Note #3
    [-]PFA-CHRG-CHRT.pdf

  12. #25
    Join Date
    Jan 2008
    Location
    Texas
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    1,855
    Agree good debate. If there is missing tube insul in a hot attic and additional refrig is added, your head would also increase. I like what the said, charge at condenser but take a look in the attic also. I think a very good point was made about proper air flow. Apts often have vents closed and dirty coils.

  13. #26
    Join Date
    Feb 2005
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    In a van by the river
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    621
    Quote Originally Posted by Itstartedasacc View Post
    What if your lineset is picking up 10 degrees of heat and your target superheat is 10 degrees. You take the temp near the compressor and add accordingly. You just moved the saturation point in the evaporator to the outlet. No change of state=no BTU gain=no cooling=hot unhappy person. Who pays for that return call?
    A pressure enthalpy chart would not agree with you. The more pounds of saturated liquid that you have in the evaporator the more heat you can absorb. The problem would be if there wasn't enough heat (or moisture) to absorb from the conditioned air. It would be ideal to have a 1 degree SH out of the evaporator with no gain on the suction line if it wasn't for that "compressor". Obviously a uncontrolled heat gain on the actual suction line doesn't help anything.
    ## + years in the field never made you a know-it-all This industry is far more diverse than you are

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