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  1. #1

    New System, Low Delta T

    My HVAC system is a 3 ton, and properly sized for my house. It is just over 1.5 years old and hasn't been right from the beginning.

    I live in NW Florida so it is very hot right now, but my system can't maintain 76-77 degrees during the day. The AC runs nonstop from 10-9 almost every day.

    The first summer I had the system, I couldn't maintain 80 degrees. So the installing contractor came out and "fixed the problem". They claimed I had a block in the filter dryer, so they swapped it out and it appeared to work. 6 months later the refrigerant line coming off the indoor air handler would vibrate violently and would keep my wife and I up at night. Once again installing contractor came out, claimed the system was overcharged, bled off refrigerant and it appeared to work.

    Now its summer again and the system runs all day long just to maintain (and sometimes it can't maintain 77 degrees). I live in a new development and an identical model house, with same layout orientation, HVAC system, insulation, etc. has no problem at all. In fact the lady living there complains that her boyfriend keeps it too cold.

    I am getting a delta T of 11.5-12.5 (as meas. directly off the plenum and return). The installing contractor came out three weeks ago and replaced the evaporator. He claimed it was a bad TXV. The system worked great for a week and half and now its back to its old tricks.

    The installing contractor has been out three consecutive days this week and if anything the system is worse than when he began. The first day he found that poor drainage caused condensate to back up into the chase pipe. THAT'S THE PROBLEM HE SAID!... Wrong, drained the line ensured its dry and still the same thing. The next two days he kept adjusting the charge, but its still not right.

    Bottom line, am I right to assume the system isn't performing right because I have a very low Delta T? Secondly, what the heck could be wrong? Gremlins maybe???
    Last edited by Orion45954; 07-15-2011 at 04:21 PM. Reason: left out info.

  2. #2
    Join Date
    May 2000
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    Indianapolis, IN, USA
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    34,098
    Without being there, hard to say. Refrigerant level, TXV, undersized ducts, attic heat gain in ducts, Need to find someone with some brains, not those who change parts on the outside chance it will solve it.

  3. #3
    Join Date
    Jul 2008
    Location
    Rochester NY
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    4,722
    Leaky ducts? If the system is running properly and all houses are identical, it's a quality issue. I'd guess some poorly connected ducts.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  4. #4
    if the dryer was indeed clogged last yr and the txv valve was bad this year and all the other issue id bet theres moisture in the system which is a non condensable ive seen many line sets ran on new construction and the guys tape the ends which doesnt stop moisture from getting in for month that the lines are there during new construction until equipment installed. Seen this many times.

  5. #5
    Join Date
    Jun 2011
    Location
    Wake Forest, NC
    Posts
    352
    a chance that one of the service techs on one of the many prior calls put R-22 in instead of 410a, screwing everything up...

    If it was my install, based on what you are telling me I would evacuate the system and charge by weight. Then take a superheat and subcooling reading to check the performance of the refrigerant system...

    Ask the contractor for superheat and subcooling readings and then post them here...

    high superheat/low subcooling = low charge
    low superheat/high subcooling = high charge
    high superheat/ high subcooling = refrigerant or airflow restriction
    It's not rocket-science...

    It's electromechanical thermodynamic engineering

  6. #6
    Quote Originally Posted by HVACTechNC View Post
    a chance that one of the service techs on one of the many prior calls put R-22 in instead of 410a, screwing everything up...

    If it was my install, based on what you are telling me I would evacuate the system and charge by weight. Then take a superheat and subcooling reading to check the performance of the refrigerant system...

    Ask the contractor for superheat and subcooling readings and then post them here...

    high superheat/low subcooling = low charge
    low superheat/high subcooling = high charge
    high superheat/ high subcooling = refrigerant or airflow restriction
    seen that before

  7. #7
    Join Date
    Jun 2011
    Location
    Houston area
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    1,493
    Quote Originally Posted by Orion45954 View Post
    .......Bottom line, am I right to assume the system isn't performing right because I have a very low Delta T? Secondly, what the heck could be wrong? Gremlins maybe???........
    No, you'd be right to assume you have a low Delta T because the system isn't performing right.


    Quote Originally Posted by ac in fl View Post
    if the dryer was indeed clogged last yr and the txv valve was bad this year and all the other issue id bet theres moisture in the system.....and I'd bet you'd be wrong..... which is a non condensable.... it is? ......ive seen many line sets ran on new construction and the guys tape the ends which doesnt stop moisture from getting in for month that the lines are there during new construction until equipment installed. Seen this many times.
    Even if the lines are taped and moisture (or more likely, vapor) seeps in, a proper evacuation will take care of it. A vaccuum pump doesn't remove "liquid" at all. It lowers the barometric pressure inside a closed system so that that H2O boils into a vapor and the pump removes the vapor. BTW - moisture IS a condensed vapor.


    It patently ridiculous to replace an evaporator because of a bad TXV. And, in a case like this where a new TXV, evaporator and filter dryer were installed and there are too many unknowns about what's really inside, I would probably recover the refrigerant, replace drier, evacuate and charge by weight. Also guys, a standard filter drier is only good for around 7 or 8 full refrigerant passes before the desicant becomes fully chelated. Anytime a system is opened the drier should either be removed or replaced.

    BaldLoonie says it best:

    Quote Originally Posted by BaldLoonie View Post
    Without being there, hard to say. Refrigerant level, TXV, undersized ducts, attic heat gain in ducts, Need to find someone with some brains, not those who change parts on the outside chance it will solve it.
    Good call!
    The picture in my avatar is of the Houston Ship Channel and was taken from my backyard. I like to sit outside and slap mosquitos while watching countless supertankers, barges and cargo ships of every shape and size carry all sorts of deadly toxins to and fro. It's really beautiful at times.....just don't eat the three eyed fish....

    `. .` .>(((>

    `... `. .` .>(((>

    .` .>(((>

    LMAOSHMSFOAIDMT

  8. #8
    Quote Originally Posted by Cooked View Post
    No, you'd be right to assume you have a low Delta T because the system isn't performing right.




    Even if the lines are taped and moisture (or more likely, vapor) seeps in, a proper evacuation will take care of it. A vaccuum pump doesn't remove "liquid" at all. It lowers the barometric pressure inside a closed system so that that H2O boils into a vapor and the pump removes the vapor. BTW - moisture IS a condensed vapor.




    It patently ridiculous to replace an evaporator because of a bad TXV. And, in a case like this where a new TXV, evaporator and filter dryer were installed and there are too many unknowns about what's really inside, I would probably recover the refrigerant, replace drier, evacuate and charge by weight. Also guys, a standard filter drier is only good for around 7 or 8 full refrigerant passes before the desicant becomes fully chelated. Anytime a system is opened the drier should either be removed or replaced.

    BaldLoonie says it best:



    Good call!
    not water though!

    try to remove liquid or excess moisture in a piston style aka hermetic or scroll style compressor and see how well it condenseshat (or changes to a vapor) If that were the case we wouldn't need refrigerant. or better put water in a car motor and see if you dont bend a rod. also your right vacum pump will remove moisture by boiling into vapor and removed by pump but will not remove water dont care how long you run pump. Ive seen taped lines full of water that literally pour out. do not hook up to these. line sets should be brazed shut and pressurized if joints in them ( if longer than 50 ft ) NOT TAPED although lots of techs do cause its easier than breaking out the torches for 5 min to braze shut.

  9. #9
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    probably why some guys like to pull vacuum overnight.
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

  10. #10
    Join Date
    May 2004
    Location
    Frederick, MD
    Posts
    955

    If I

    had a new system that "hadn't work right since day one", I would have the installation company on speed dial. If this is a brand new home, I would also notify the general contractor and get them involved as well.

  11. #11
    Join Date
    Mar 2011
    Location
    Edna Bay, Alaska Highest concentration of black bears in the US
    Posts
    623
    I have seen new installs with low delta t and poor humidity removal due to the fan speed not set up right. A lot of times the indoor unit can be used for several different sizes of outdoor units, and the fan speed needs set up accordingly.

  12. #12
    Join Date
    Jul 2010
    Location
    georgia
    Posts
    562
    sounds like maybe the run around or the company is at a loss.

    Have you talked to the service manage and/or the owner? Sometimes the top guys dont know that their team is falling down.

    If you have and you still feel you are getting nowhere and you feel that you have depleted most options and have been beaten down, then one thing one might do is submit their concerns/complaint in writing (registered mail) to the company (service manager and owner) and request a written, detailed explanation of whats wrong and what they intend to do to correct it, and in what timeframe. Also stipulate that if they fail to make adequate repairs by the deadline you reserve all rights to get another company to come out and make repairs which will be reimbursed to you by company #1, and that any and all work done by company #2 will not void any warranties/guarantees currently in place by company #1.

    also, have you checked your company out on Angie's list, Yelp, Kudzu, or even twitter/facebook. You may want to post some of your experiences there.

  13. #13
    Join Date
    Jul 2008
    Location
    Rochester NY
    Posts
    4,722
    I'd be careful about posting hvac complaints until you know the culprit is the equipment.

    Maybe there is missing panning, a thermal bypass above a stairway or soffit, or some other unknown deficiency causing/contributing to the problem.

    Hvac is not always the solution, and it's not always the problem.

    If you think the hvac wasnt done right in your new house, why do you think everything else was done right?
    Which makes more sense to you?
    CONSERVATION - turning your thermostat back and being uncomfortable. Maybe saving 5-10%
    ENERGY EFFICIENCY - leaving your thermostat where everyone is comfortable. Saving 30-70%

    DO THE NUMBERS! Step on a HOMESCALE.
    What is comfort? Well, it AIN'T just TEMPERATURE!

    Energy Obese? An audit is the next step - go to BPI.org, or RESNET, and find an auditor near you.

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