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  1. #1

    New Central AC system not reaching setpoint

    I have a 2 story home and have 2 separate systems for each floor. 2.5ton lower and 3 ton on the upper floor. It is located in the actic with the return in the main hallway (20x20) and a 6" supply in each bedroom and bathroom (7 total).

    I had to have the compressor replaced because the moron contractor I used in the begining mis-matched the 2.5 ton air handler w\ a 3tons compressor! Well that lasted 4yrs, remarkably. The guy who did the work last fall did a very good job, you can see the difference in quality of his workmanship alone. So new air handler and compressor, and he added 2 supplies to get the proper CFM's.

    So anyway it has been 90+ degrees and very humid the past couple of days. This is the 1st real hot spell since the install. And even though the unit may have been mis-matched before it always was able to cool the 2nd floor to 68 degrees no matter what the outside temp was. Now with the outside ambient temp at 93 it will not bring my 2nd floor to anything lower than 77. Even when the air at night dropped to 72 it took 4 hours to drop from 77 to 70.

    I called the contractor up and he came right over to check things out. Right there is the sign of a great contractor, it was a Saturday evening. So the intake air was showing 80 and the output of the air handler was 60. So he is basically telling me that a 3 ton system will not cool 900 sqft to 68-70 when it is 93 degrees outside. Does this sound right?

    What are my options? I need to get better than 77 degrees on my 2nd floor when it is hot outside. Not to mention the unit is now running 24\7 without ever shutting down!

    Any input would be appreciated. TIA -Vince

  2. #2
    Join Date
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    you have a 3 ton system for 900 sq/ft????

    Time fore some serious insulation.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

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  3. #3
    Join Date
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    are the windows open??

  4. #4
    Join Date
    Feb 2008
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    Quote Originally Posted by Pascone10 View Post
    are the windows open??
    dur dur dur dur

    I was wondering why there was a cool breeze outside with no wind

    He's just doing his part to prevent global warming
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  5. #5
    So I take it that there is definitely a problem wit this install......

    Like I said even with the mis-match 2.5ton compressor and 3 ton air handler it had before it always cooled the house down very quickly no matter what the outside temperature.

    This is just getting very aggravating because the builder picked a crook the first time and I paid $xx for the down stairs unit and upstairs. Now I picked a guy that my father had good luck with for 30 years and another $xx later I still have a system that will not cool my house good enough.

    Is there anything in particular I should ask my contractor to look for? The house is only 4 yrs old and has R30 insulation in the attic and 2x6 walls w\ R15. Upstairs and downstairs are separate air handlers and compressors. I was more comfortably w\ window units and they cost much less.

    -Sorry was looking for more informative answers than are your windows open. Just looking for a site that might have some professionals that may be willing to share a tip or two. Smart ass answers are easy to come by.
    Last edited by smallie_seeker; 06-09-2008 at 02:40 PM.

  6. #6
    Join Date
    Sep 2005
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    Bay Area, CA
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    843
    If theres a problem with the install call the installing contracter out? Theres no magic button on these systems that you can flip to fix them.

    You can pair a 3ton airhandler to a 2.5ton condenser its common.
    Global Warming or: None like it hot
    No pleasure, no rapture, no exquisite sin greater... than central air. -Dogma

  7. #7
    Join Date
    Feb 2008
    Location
    Western NC
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    you need to remove your prices as they are not allowed.

    You should call the contractor back and ask to see the load calculation. Something tells me that one wasn't done.

    I hate the rule of thumb but the rule of thumb is 1 ton per 600sq/ft. You have 900. So according to rule of thumb (which I don't use), your nominal system is a 1 1/2 ton.

    Now, that being said, its an upstairs unit. More need for A/C than heat. So a 2 ton would be my first opinion without a load calc. A 2 ton system with a 5 KW heater would probably be a bit closer than what you have.

    And oversized system should shurly cool the space. It won't draw any humidity out and will short cycle until its early death. So it sounds like another issue.

    Possibly your heat strips are running with the AC and contridicting itself. Maybe your ductwork isn't sealed properly. The list is long.

    You need to find a reputable contractor. HVAC is not the "doin it cheap" industry. If you expect your system to work, you need to spend the money.


    Also, did you say the system you replaced was only 4 yrs old????? with a dead compressor? That compressor should have been under a part warranty. The cheapest route in that case would have been a new compressor under the warranty and the properly sized AHU. Not an entire system. Just some FYI for you.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  8. #8
    Join Date
    Nov 2004
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    Thibodaux, LA
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    What so you have now? 2.5 ton condenser/compressor or 3.0ton?

    Your compressor may be cycling off. I could be something very simple.

    Have your contractor return during the week to check it out again.
    "Football Season again finally"

  9. #9
    Iraqvetran,

    Thanks for the information, you are 100% right you get what you pay for, but unfortunetly I got no price break and still got screwed! The 1st guy who screwed me was through the builder, I had no choice who to use. And you figure they build 100's of homes a year they guy should be good.
    I agree with you that you would expect with a 3ton condensor and 3 ton AHU it should cool better now than when it had a 3 ton condensor and 2.5 ton AHU. Sorry I made a typo in the original post. The 1st contractor had a larger condensor than AHU. But the fact that it cooled so much better than it does now has me very surprised.

    So, what you suggested is what I had done. New compressor (3 ton) and New AHU ( 3 ton) Although the compressor was not covered under warranty because of the mis-matched condensor and AHU. The new contractor reused the ductwork as he said it was done correctly (believe it or not). The only thing he did was add 2 more 6" supplies to match the return size.

    It is a heat only unit, no heat strips.

    So I will def ask my contractor about the load calculations. But I just do not understand how a mis-matched 2.5-3 ton system worked so much better than a true 3ton.

    Thank you very much for the information you have given me.

    -Vince


    Quote Originally Posted by green jumper View Post
    If theres a problem with the install call the installing contracter out? Theres no magic button on these systems that you can flip to fix them.

    You can pair a 3ton airhandler to a 2.5ton condenser its common.
    Green Jumper,

    Not looking for the magic fix me button, just trying to get some ideas to jog my contractor's memory. I did call the contractor out and as I wrote in my original post he even came out on a Saturday to look at it. But his answer to me was that the intake air was 80 degrees and the output was 57-60 degrees so it was doing its job by dropping the air by 20 degrees. But my problem is that my upstairs is only 960 or so sqft and with this 3 ton system I am only seeing 77 degrees inside when the outside temp is at 93-95.

  10. #10
    Join Date
    Jun 2001
    Location
    Louisville, KY
    Posts
    12,172
    Is this a Cape Cod with lots of knee walls on the second floor?

    How about a picture of your home from the front and side?

    Also, a few pictures of the attic installation would be handy.
    Perhaps you should have read the instructions before calling.

  11. #11
    I will take the pics as soon as power comes back on! T-storm just went through and the wind must have knocked down a power line......

    No knew walls, it is a colonial style 2 story, 9\12 pitch roof so plenty of space in the attic. I will get the pics up ASAP.

    -Thanks

    Quote Originally Posted by jrbenny View Post
    Is this a Cape Cod with lots of knee walls on the second floor?

    How about a picture of your home from the front and side?

    Also, a few pictures of the attic installation would be handy.

  12. #12
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    Quote Originally Posted by smallie_seeker View Post
    So, what you suggested is what I had done. New compressor (3 ton) and New AHU ( 3 ton) Although the compressor was not covered under warranty because of the mis-matched condensor and AHU. The new contractor reused the ductwork as he said it was done correctly (believe it or not). The only thing he did was add 2 more 6" supplies to match the return size.
    Something doesn't seem right there. Systems are matched like this a lot. It all depends on the application. That should not have really voided your warranty as it was installed by a contractor. I may be wrong here but I feel your warranty should be good.
    I fully support the military and the War on Terrorism.


    If you don't know, then don't do. If you don't know and still do, then be prepared to pay someone else a lot to undo what you did and then do it right.

    If you do know, then do. But do it right. Otherwise, you may not be doing it long.

  13. #13
    Join Date
    Jan 2001
    Location
    Pamnyra VA.
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    710
    seems 20x 20 is a little light for a 3 ton return.

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