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  1. #14
    Join Date
    Jun 2004
    Location
    Earth, 20th century, North America, Texas. HVAC tech in late 70s.
    Posts
    290
    Originally posted by mpatrick
    Just to calibrate what I mean by high electric bills.

    $543 last month for a 2700 sq ft house in Houston. Rate is 11.1/kwh, usage is average of 145kwh per day. Other large loads have like the pool pump etc have been investigated and every thing points to this unit as the energy hog.
    Whuh ! I live in Houston and my last summer bill was ~$200/month and my wife complains it's high (2300 ft2 1-story 5-ton AC, trying to keep @ 78F , <50%RH). I feel your pain.

    On the elect. rate, on the Reliant bill, ~7c/KWh, but watch out the "energy cost" line, additional ~5c/KWh and this would change as fuel cost goes up.

  2. #15
    Join Date
    Feb 2004
    Location
    Midwest
    Posts
    9,932
    It does sound possible that the unit's a little overcharged.

    It also sounds like your thermostat habits could be part of the problem, depending on the number of degrees of setback you're trying to use and the number of changes per day, and the setpoint of each thermostat in relation to the setpoint of the other thermostat. You could be creating higher latent loads on the system.

  3. #16
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    Rheem requires a txv on an 11seer a/c unit. With a RCBA 4878 coil it only gives you 10.5 seer. Your superheat is way to low it should be a 54 deg SLT at parameters given.

    [Edited by karsthuntr on 07-01-2004 at 08:23 PM]
    Karst means cave. So, I search for caves.

  4. #17
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    I matched a couple of Benchmark coils with Rheem heat pumps and had low suction and low delta temps. on both. Nothing I could do would correct the poor performance. Now I will only match a TXV Rheem coil against their heat pumps or condensers, if a Rheem OEM piston coil is not available.
    There is nothing more frightful than ignorance in action....Mark Twain

  5. #18

    Decision Made

    I have decided to replace the evaporator coil. I will be installing a new coil with a TXV this weekend.

    Before anyone asks:
    1. I have CFC universal certification (got it years ago)
    2. I will recover refrigerant (borrowed recovery unit from work)


    Thanks for all of your help and opinions.

    I will post the results and performance when I return from vacation in 2 weeks.
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

  6. #19
    Join Date
    Mar 2002
    Location
    Richmond, Virginia
    Posts
    4,264
    I bet you will be amazed at the difference!
    There is nothing more frightful than ignorance in action....Mark Twain

  7. #20
    Join Date
    Jun 2003
    Location
    Florida
    Posts
    9,548
    I may be off-base here, but with a "hacked in coil" you might actually have a 6 seer instead of a 11. Depending on age/condition of condenser, either replace with a real high effeciency unit or just a match A/H for that condenser. If you think all signs point to this a/c, and it's costing you $500+/month,I wouldn't hesitate to replace it. Make sure you have duct system evaluated. You're right about 11 DT, that's not good.good luck.
    If everything was always done "by the book"....the book would never change.

  8. #21
    Join Date
    Jul 2001
    Posts
    1,864
    Originally posted by lmtd
    First guess, and it is a PUNT, overcharge.

    Need more data.

    Air entering condenser
    Air leaving condenser
    Saturated condensing temperature (psig is fine if you do not have a saturation chart)
    Liquid line leaving condenser
    Liquid line at metering device (about 6" in front of it but after all accessories, right before it enters the air handler)
    Air entering the evap
    Air leaving evap
    Suction saturation temp (psig is fine if you do not have a saturation chart)
    Suction line temp at the evap (leaving air handler)
    Suction line at the compressor (condenser service valve works too)
    Compressor Amperage actual reading
    Compressor RLA or FLA from the modle plate.

    Get it all at the same time and you will get what you seek.
    This will only take you 1/2 an hour, it would be nice to see the numbers before you change the coil.

  9. #22
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,959

    Re: Decision Made

    Originally posted by mpatrick
    I have decided to replace the evaporator coil. I will be installing a new coil with a TXV this weekend.
    Don't forget that hard start for the condenser with that txv.If that's a recip. it will bust a gut trying to crank-up.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  10. #23
    Join Date
    Feb 2004
    Location
    Midwest
    Posts
    9,932
    Hackety hackety hack
    a chill ran up my back


  11. #24
    Join Date
    Sep 2003
    Posts
    1,311
    Originally posted by mpatrick
    Expert opinions please:

    Outdoor Ambient 78 DB 66WB
    CFM 1585
    RAT WB 65
    Evap TD 11

    Condensing Unit
    Suction P 59
    Liquid P 199
    Superheat 12
    Subcooling 22
    FLA 19.9 - Unit running at 18

    Evap coil is fixed orfice.
    With the numbers provided the unit is overcharged according to the superheat (should be about 18°), overcharged according to the subcooling, but the 59# suction pressure and 11° evap TD indicates that there is something more than just an overcharge. I would vote looking for a restriction such as a kink in a line or a plugged refrigerant filter/drier.

  12. #25
    Join Date
    Feb 2003
    Posts
    538
    I had a goodman unit do something similar to me. Superheat was crazy low, pressures low, subcooling high, only a 10* drop across the coil. Tracked it down to the distributor tubes to the left side of the coil were totally clogged. Was only feeding 1/2 of the evap. Been in there 2 years, last guy just charged the hell out of it to get the pressure up.

  13. #26

    Coil Changed

    Changed the coil today.

    16 degrees across coil
    11 degrees superheat (of course TXV)
    12 degrees subcooling

    Evap pressure 72
    High side 225

    I will post complete results next week when I return from vacation and can hook up the service tool I borrowed from work to take the original readings. I want to be able to chart the data against the data I took before the change.


    I did notice that the coil I removed had a leak repair done/attempted at the u-tube, I suspect they plugged it full of solder. I was going to cut into it to verify, but my wife insisted that it go to the curb since today was trash day.
    Mike Patrick
    The opinions stated here are mine and may not reflect those of my employer Siemens Industry, Inc.

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