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  1. #14
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,121
    Quote Originally Posted by just_opinion View Post
    You seem to have more common sense than the tech who recommend replacing the TXV with piston.
    +1.....
    __________________________________________________ _______________________
    “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

  2. #15
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    OK some fresh stats... It's pouring rain in Houston today so the outside temp is substantially lower than it has been, currently 75 deg. Indoor temp is 77 with a RH of 42% (per the nice Herman Miller retirement gift hanging on the wall). The current draw (Fluke 87 w/80i-410 current probe) says currently 9.0 amps, return air temp is 76 and register air discharge is 52 (per RayTek MT6 thermal gun). Based on all this appearances are it's working today, though it's not hot outside.

  3. #16
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,121
    Quote Originally Posted by Cap'n Preshoot View Post
    OK some fresh stats... It's pouring rain in Houston today so the outside temp is substantially lower than it has been, currently 75 deg. Indoor temp is 77 with a RH of 42% (per the nice Herman Miller retirement gift hanging on the wall). The current draw (Fluke 87 w/80i-410 current probe) says currently 9.0 amps, return air temp is 76 and register air discharge is 52 (per RayTek MT6 thermal gun). Based on all this appearances are it's working today, though it's not hot outside.
    42% RH is low, we try to shoot for around 45-50 % but it's your sinus infection.
    __________________________________________________ _______________________
    “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

  4. #17
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    5,031
    Quote Originally Posted by Mr Bill View Post
    Darrell, that's because he has it overcharged, from here all I saw was, he might have just needed the tech to check the SC and adjust the charge accordingly, but I have been wrong once before.
    Mr. Bill, you are on target; I was just getting ready to post that quite obvious point to a good troubleshooter.

    If the Return-Air is still at 80F the Ambient at 95F; the condenser temp-rise should be around 17F not 22-F; the suction should be around 130-psig not 140.

    He says the indoor temp is at 76-F; if that were the return-air temp the head should be around 351-psig or 107-F or only a 12F temp-rise; suction 129-psig or 44F.

    Find out what the subcooling (SC) should be & check it; I'm betting it has too much SC.

    Further tests might also reveal some Non-condensibles in the refrigerant system...
    Last edited by udarrell; 08-19-2012 at 12:52 PM. Reason: Missing word...

  5. #18
    Join Date
    Dec 2007
    Posts
    4,763
    Thermal gun type not the best for getting actual air temps, you should try a probe type thermometer.
    The Food Stamp Program, administered by the U.S. Department of Agriculture, is proud to be distributing the greatest amount of free meals and stamps EVER.
    Meanwhile, the National Park Service, administered by the U.S. Department of the Interior, asks us to "Please Do Not Feed the Animals". Their stated reason for this policy "... the animals become dependent on handouts and will not learn to take care of themselves."
    from an excerpt by Paul Jacob in Sun City, AZ

  6. #19
    Join Date
    Dec 2002
    Location
    Houston,Tx.
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    16,121
    Quote Originally Posted by Cap'n Preshoot View Post
    return air temp is 76 and register air discharge is 52 (per RayTek MT6 thermal gun). .
    Not the proper way to check TD, you need a temp. meter with a probe, and it needs to be checked as close to the R/A @ the air-handler or furnace as possible, and checked at the air plenum secondary side of the evap. coil. this will get you a true TD.
    __________________________________________________ _______________________
    “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

  7. #20
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,754
    Quote Originally Posted by Mr Bill View Post
    Ok I am not Mr. Rocket Scientist here as for as air flow, but how does it act as a "fresh air" duct and also help to hold a positive air pressure in your home? Maybe one of the air flow experts here can explain this one to me.
    Dominant supply duct leakage to outside of thermal envelope cause a neg pressure inside the therm env and dominant return air leakage outside the therm env causes the inside to be a positive pressure. By ducting some of the return air from outside you are introducing "fresh air" to the system and putting the house into a positive pressure

  8. #21
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    Quote Originally Posted by Mr Bill View Post
    Not the proper way to check TD, you need a temp. meter with a probe, and it needs to be checked as close to the R/A @ the air-handler or furnace as possible, and checked at the air plenum secondary side of the evap. coil. this will get you a true TD.
    Tech did that Friday evening, went into attic with temp probe and inserted it (punctured) the RA line and right at the first duct closest to the coil. Yes, he put tape over the punctures...
    Problem seems to show up when it's hotter than blazes outside. Today with outside temp of 75 it's about to freeze us out, cooling extremely well. Not much AC experience from broadcast work but logic suggests maybe a hole in one of the RA ducts in the attic. Both RA grilles have enough suction to hold a sheet of paper tightly to them but doesn't rule out sucking attic air on a hot day (when we're having the most trouble)

  9. #22
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,121
    Quote Originally Posted by jtrammel View Post
    Dominant supply duct leakage to outside of thermal envelope cause a neg pressure inside the therm env and dominant return air leakage outside the therm env causes the inside to be a positive pressure. By ducting some of the return air from outside you are introducing "fresh air" to the system and putting the house into a positive pressure
    Thank You! Thank You Very Much!
    __________________________________________________ _______________________
    “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
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,121
    Quote Originally Posted by Cap'n Preshoot View Post
    Problem seems to show up when it's hotter than blazes outside. Today with outside temp of 75 it's about to freeze us out, cooling extremely well.
    Quote Originally Posted by Cap'n Preshoot View Post
    System pressure showing 400 psi high side and 140 low side.
    This above is what concerns me the most.
    __________________________________________________ _______________________
    “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

  11. #24
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    As a (probably unrelated) aside, we use only MERV-8 media filters (20 x 25 x 4.5). Our old AC guy (same company before changing hands) told us anything much higher than MERV-8 is unnecessary plus the higher filtration reduces air flow & puts static load on the blower potentially causing it to overheat & prematurely fail but register discharge temp would be incrementally cooler. Does any of that make sense?

  12. #25
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,754
    Overcharge, dirty cond coil weak cond fan motor will cause problems of high head pressure in the heat of the day and unit will not cool very well under those conditions.

  13. #26
    Join Date
    Aug 2012
    Location
    Katy, TX
    Posts
    50
    The Tech *purposely* added addt'l coolant based on what he determined was low current draw. He had his manifold guages attached along with amprobe (which agrees w/mine) and incrementally added more coolant until the current draw got up to what he thought it should be (11.2 amps) while watching his gauges and stopping at 400 PSI. This was the only way he was able to get the temp differential even close too what it should have been. I think he got it to around 12 deg. He said the current draw should have been 80% of RLA (14) rated amps. He was not happy with the result, which led him to believe that maybe the TXV was defective and wanted to come back another day (no add'tl svc call chg) to remove the TXV and put in a piston. Swapping the TXV for a Piston is what prompted me to come to this group for another opinion.

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