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  1. #1
    Join Date
    Jun 2005


    I recently had a new A/C and Furnace installed in my split entry home. I can't get the thermostat to get below 72 unless it is well into the middle of the night even when the set tempature is well below 70. The unit runs essentially all day and typically cannot get below 74. This is actually better then when it was first installed a few weeks ago. Initially, the thermostat would read 78 on a day that was barely 80. The service guys indicated that one of the techs put too much PURON in the unit. After 2 1/2 hours they indicated that reducing this level would solve the problem. It did make it cooler but now it still runs all day and averages 74-75. When the sun hits the front of the house from 6PM until dark, it can go even higher especially if there are more than two people in the house.

    I am very dissapointed by this and wondered if there was any help out there or something I can ask the service guys who typically say that 75 is an acceptable temp.

    My old unit was from 1987 and was the same nominal ton (2 ton - 24,000 BTU) so you would assume that a 2005 unit would perform the same if not better. My old unit could easily get down to 70 and sometimes under.

    The new units are a Trane XV80 and a 2 ton SR12. I live in Pittsburgh, PA (NorthEast USA). We have had some hot days at 85 and decent humidity. If my unit can't handle these days in June, what is it going to do in August when it will be reaching 90 and 100% humidity!

    My house is a split entry and is about 1,500 square feet. The outside of the house is 42' x 26.5'. It is a split entry, so the game room 10 x 20 is essentially negligable since the rest of "first floor" is garage.

    The service guy is coming out again soon and of course the highs in the next few days are below 75 so they are not going to see the problem. I went with the place because they were reputable and are part of the @Home services from Home Depot. But they are giving us lines like "need more returns", "The A/C is designed to cool 15 degrees less then outside", and "75 is an acceptable tempature".

    During the sales process, I asked the sales guy a number of times if I needed to bump up the tonnage, need more returns, etc and the pitch was very convincing that the new unit would be everything I could ask for since it would be 15 years newer technology. They even added a return in my game room, so the song and dance about not enough returns is bull. Plus, my old unit was able to do 70 and did not have to run all day. The new unit runs 16+ hours a day and can't get it to 72 unless that is what the temp is outside or less. If it matters, the tech guy indicated that it was "68 degrees on the coil".

    I have seen on some threads doing temp measurements at the vents and returns, what are the expected values?


  2. #2
    Join Date
    May 2002
    Keeping the temperature at 70 °F is just asking for mold problems, depending on the construction of your house and the outdoor dew point. You should try to keep it at 75 °F or higher.

    Does your system have a TXV?

    Do you happen to know what the pressures and temperatures were when they decided the system was properly charged?

  3. #3
    Join Date
    May 2004
    2 tons for 1500 sf sounds small. I have 2.5 tons for a non-insulated 1000 sf house and at 90deg and high humidity the best I can get is 75 indoor. At night I can get down to 72. Unit will run non-stop. I am planning to insulate my ducts this summer, which should help. Not sure what the heat gain is but my load calc says you loose 5000 btu of heat with uninsulated ducts. You can check temp drop across the coil. Should be about 15 to 20 deg.

  4. #4
    Join Date
    Jan 2004
    It may still be over charged.

    A 68° coil is to warm for a 85° day when the unit has been running all day.

    Ask them if you have a piston, or txv metering device.

    Also ask them what the indoor wetbulb temp, and outdoor drybulb temp is. Ans what the superheat, and subcooling is when they recheck you system.

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    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    Sep 2001
    Vancouver Canada
    Sounds like an overcharge still, do you have an exceptionally long line set? I would question how the unit became overcharged. On an 85 degree day you should have no problem pulling the temp down to 72 to 75 degrees if your old unit would do it and you have not made any major changes. Get the service guy to check all the usual temps and pressures and then post the results.
    "Go big or Go Home"

  6. #6
    Join Date
    Mar 2002
    Concord, CA
    "so you would assume that a 2005 unit would perform the same if not better"
    Bad assumption. Nominal tonnage and actual tonnage are different things. They may have been the same nominally but not in reality. Sensible/latent ratios will be different as well. One system may remove humidity better than the other. The more energy a system spends on removing humidity the less it can reduce temperature and vice versa. The way you deal with that is to do a heat load calculation. That would have told them how much sensible and how much latent capacity they needed. Then they could of picked the equipment with output that matched what you needed. Depending on what the old system was rated at was stupid. Telling you that advanced technology will save the day was even more stupid. Old systems chilled the air. Technology has done NOTHING to improve that except make it cheaper to do so. In fact, in some respects it’s made things worse. In order to save money they make these things in ways that don’t remove humidity as well as they use to. So then they have to sell you all sorts of fancy controls crap to make it remove humidity like the old ones did without all the fancy crap!!!

    "The A/C is designed to cool 15 degrees less then outside"
    That's an absurd statement from a tech scratching for answers. There's no such standard. An AC can cool much more than that or less than that. It's variable depending on how hot it is inside, outside and what the humidity is.

    Here's MY ultimate answer to knowing whether or not a system is delivering what it's supposed to. Have them measure what it's delivering!!! Man this stuff irks me. All new systems I put in get their exact output measured. All you have to do is measure the airflow with an airflow hood, measure the temperature and humidity entering system and then measure the same as it leaves the system. There are very simple formulas you punch those numbers into to determine EXACTLY how much sensible and how much latent capacity you have. If the system is not delivering its rated capacity, I'd tell them to make it deliver or they'd see me in court. If they say they need to add returns to make that happen then you tell them they should have said so up front.

    This hacker BS where they just slap equipment in and hope for the best bugs the crap out of me. There should be no hope. They should have MEASURED it. For all the bumping into each other they've done I can guaran-damn-tee you they haven't bothered to measure the system’s output. They probably don't even know how to measure it.

  7. #7
    Join Date
    Jun 2005
    I very much appreciate all of the responses.

    The air conditioner is a Trane XR12 2TTR2024A 2.0 24,000.

    After my attack dog wife ripped into the president and service people, they said they would come out again, but not call yet. This is OK as they can come next week when the temps get back up to 80+ outside.

    Last night at 8:30PM, it was 72 out with 63% humidity. I had the temp set at 70 and it ran but could not get down below 72/73. It was cooler outside than it was inside!

    Regardless of mold and other environmental factors, 72 is the maximum tempature I feel is comfortable (most extended family members have theirs at 70 or below). I think 72 is reasonable to think my unit should obtain. My office at work is 67 and now that is cold.

    So what exactly can I do to determine things? I don't know what the "usual temps/pressures" or other things are. If I have a piston or txv, what can I do with that? When they come back, what specific things should I ask them about? The more knowledge I have, the more leverage I have to get things working.

    I don't have any pressure or other values to give at this time. As far as the too much refrigerant, here is how that came to be. They installed the system in May. At that time, the temps in West PA were lower than average and maybe got into the 70s but were in the mid 60s. So they came back to "start up" the system. The service guy fiddled around for at least an hour and a half and that was that. Then the temps in West PA started rising and I saw 78 on the temps inside, so I called. The service guy came out at 8:30 in the morning and after 2 1/2 hours gave the dance about too much refrigerant and the previous tech guy not knowing about the new PURON units being different as he implied you could put more pressure in the old ones I guess. So instead of 78 I got 72 when he left at 10:30 but it wasn't mid-day yet. The temps were acceptable 73-75 the rest of the week, but from 6PM-9PM the hottest time of day in my house since sun sets on front the temps shot back up to 78 when I had some family over (6 people). We haven't had a really hot day since to compare.

    The system does have a longer line set to the unit outside but I was "assured the longer line will make no difference". The line goes into my garage and then on the side of the house. The total distance is probably 25-30 ft at max since the entire house span is only 42 feet.

    I went with the place I did since they have a good track record for 30+ years and they are in tied with the big home improvement chain assuming that I would get better service when this type of thing happens.

    As a side note on the size, I had 3 quotes before I had this installed and all three places pretty much had the same size equipment but of lesser brand name then Trane. They seemed more "used car salesmen" to me which is why I did not go with them. The only place that indicated I should go with a 1/2 ton larger unit for the A/C never returned my calls or quote in writing.

    If they ultimately did not place a powerful enough system in my home, is there any action I can take? Can I have them remove everything for refund (does not benefit either party)? Can I have them install a more powerful unit (and split difference on cost)?

  8. #8
    Join Date
    May 2002
    If the technician put Puron into your system he made a BIG mistake. A Trane XR12 2TTR2024A is an R-22 system.

  9. #9
    Join Date
    Dec 2002
    Rochester, MN
    I agree w/ Pan..

    XR12 is NOT a "Puron" system.. R-22 it is.

    Also, Make sure the dealer has the dip switch set right on the furnace since it's a XV80.

    Dip switch set at 2 tons?

    How many CFM per ton?

    Comfort-R turned on?

    I used to have my ac down to 72, now I have the XV and comfrot R, I found out that way too cold.. I turn it up now to 76-78..

  10. #10
    Join Date
    Dec 2002
    peoples republic of maryland
    I second Panama, that is an R-22 system reqiring a .057 piston. What is the indoor coil number, and does it have an expansion valve?
    "The meek shall inherit the earth"
    "he that's walking with wise persons will become wise, but he that is having dealings with the stupid ones will fare badly" Proverbs 13:20
    "Pressure is something people feel when they don't know what their doing". Peyton Manning-superbowl MVP

  11. #11
    Join Date
    Jun 2005
    Again, thanks for everyone responding.

    First of all, I made a mistake. My a/c unit is an XR12, but it is the 4TTR2024A which is an R410 and not a R22. So sorry about that. Much of my post was related to thinking they were putting R410 in a R22 unit so we'll disregard that. My furnace is an XV80. Its model number is TUD080R9V3K4.

    Much of this is dealing with dip switches. For what the dip switches mean in my front panel take a look...

    My dip settings

    DIP 1 and 2 appear to control the A/C unit size.
    After looking at the dip switches, I have some potential concern. First, if you buy into the dip switches, it appears that the model of furnace I have can handle a 2.5, 3, and 3.5 ton unit. The setting of the dip switches for 1 and two are both up/on which on the setting panel says --. Is that assumed to be a 2 ton? Is it assumed you should not use a 2 ton or less unit! Should I turn dip 1 off (or have them do it?) so that it thinks it is a 2.5? I believe if you set this too high it can freeze the lines correct?

    DIP 3 and 4 appear to control the speed of the fan
    Mine are 3=on 4=off, so it appears to be on high or 450 CFM/Ton. Out of all the switches, this is probably the only one I agree with.

    DIP 5 and 6 appear to be cooling off delay options
    Mine are 5=off 6=off which is "none". Other options are 90sec, 180 sec, and Comfort-R. Should this be set for Comfort-R? From my research, this supposedly reduces more humidity, but another source indicated that Comfort-R has no real purpose with a continuous fan which is what my XV80 is.

    DIP 7 and 8 appear to be the heating settings
    7=on and 8=off which is which is "normal" or 900/1250.

    Two Stage thermostat?
    I have a Hunter thermostat. Could that be causing any issues? Should I get a Trane two stage thermostat?

    Thermostat wiring
    W2 and W1 are wired together.
    White goes to W1, and Red, Green, Yellow are color match to the appropriate color wire and terminal to the thermostat. A White goes to Y and red goes to YLO and then goes to the condensing unit outside.

    What should pressures be? Can I do any tests? I have an electronics background so I am comfortable with just about any data gathering or testing that I can do.

    Thanks again!


  12. #12
    Join Date
    Dec 2002
    Rochester, MN
    I'd turn on 5 and 6 for Comfort-R.. It will ramp the system up slowly, and also I think it does a good job..

    Like I said in my last post, I used to run A/C at 72, now w/ comfort -R, I turn it up to 77 since it does dry out the air.

    Forget the fan "ON" in the summer it just adds more humidty in the summer when the a/c turns off.. I run mine "ON in tthe winter/spring/fall. and Auto in the summer.

    Are you able to run another set of wires up? Get a REAL 2-stage t-stat to get most of your 2-stage heating.

    The Ylo and Y wire is not wired up don't have two stage cooling.. Just Y to the outdoor unit, and from t-stat.

    Also, jumper between Y and O

  13. #13
    Join Date
    Apr 2002
    First, if the furnace is not designed to handle units less than 2.5 tons, then the installer did you a disservice installing this combination.

    Second, why do you think setting the airflow to HIGH is best? This is not necessarily the case ... if your ducts are not sized to handle that airflow then the pressure in the system will not be correct.

    Personally I would not play with any settings myself; the installer is responsible for getting the system to operate properly. I'm in total agreement with mayguy -- if your system is properly sized and operating correctly, you should be comfortable at higher settings than 72. I have an XV80/XL14i combination and never set the thermostat lower than 76 (typically keep it at 78).

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