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  1. #1

    AC guy wants us to replace our entire system, do we really need to?

    We live in Texas, and these days its 103F-110F outside. We keep our thermostat set to 78F during the day and 76F at night. In this heat it is struggling, and the temperature climbs through the day until at about 6pm its 84F despite the unit staying on constantly.

    I measured the temperature at the intake and one of the vents, and the difference was 21F (78F-57F), which I believe is a good temperature differential. I was advised that it must be entire insufficient capacity in our AC unit, or poor insulation, but we've had quite a bit of insulation work done so I don't think its that. Our home is 1,700 sq/ft.

    So we got a local AC company that had good reviews online to come and look at it. This is his diagnosis "verbatim":

    "System is mismatched, 3 ton condenser, 50,000 BTU Furnace with 4 Ton Coil".

    It seems that whoever installed the system in the first place, and possibly some total morons hired by our home warranty people who replaced our furnace last year, have mismatched the various components of our system.

    The cure? We'd need to replace our entire system, at considerable cost.

    The AC guy seemed competent, but I have to say that it makes me a little concerned that the remedy just happens to be the most expensive possible option.

    Is this guy taking us for a ride or do we really need to spend this much to fix our system?
    Last edited by sanity; 08-31-2011 at 06:28 PM.

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,411
    Couple things...

    First of all, pricing is not allowed here. Please remove the prices from your posts.

    A matched system is very important to proper operation and overall comfort.

    Post the numbers on any tags at the indoor and outdoor units and someone here can verify if it is a match for you.

    The question I'll ask...

    Has the system ever worked properly?

  3. #3
    Join Date
    Jun 2009
    Location
    Albuquerque NM
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    2,484
    If you post model numbers, the guys here could probably provide more guidance. You might also have problems with insufficient ductwork.

  4. #4
    Join Date
    Feb 2009
    Location
    Portland OR
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    1,942
    Quote Originally Posted by garya505 View Post
    If you post model numbers, the guys here could probably provide more guidance. You might also have problems with insufficient ductwork.
    The ductwork is probably where you should look too. However you can usually match a 4 ton coil with a 3 ton condensor, what bothers me is that your 50,000 BTU furnace is probably a 2 ton blower so you are not getting enough airflow. You need at least 1200CFM(3 ton blower) to properly operate that AC. If either your blower or ductwork is sized improperly(or both) this could be the cause of the problem. You might be able to retrofit something like an Evergreen ECM motor that can do 3 tons of air if the furnace and ductwork can handle it.
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
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  5. #5
    Join Date
    Aug 2011
    Location
    Chicago
    Posts
    51
    You obviously have problems with the system if you are happy with it why did you call in a pro. I am not a car mechanic I trust my mechanic I do not go on car mechanic web sites. He tells me what's wrong and fixes it. Same as We HVAC pros do with our customers

  6. #6
    First of all, pricing is not allowed here. Please remove the prices from your posts.
    Sorry, done.

    A matched system is very important to proper operation and overall comfort.
    If what he told me is accurate, is my system so badly mismatched that it could cause this problem?

    If you post model numbers, the guys here could probably provide more guidance. You might also have problems with insufficient ductwork.
    Unfortunately the only component that has easily visible identifying marks are the external condenser: http://dl.dropbox.com/u/13093/IMG_20110831_173135.jpg

    The other components have no easily accessible labels, and due to a medical condition I can't get to the other side of them where those labels might be :-(

    I am fairly willing to believe what the guy said though, he seemed pretty trustworthy, I doubt he'd outright lie to us in a way that was provable.

  7. #7
    @Jimmyhat597

    You obviously have problems with the system if you are happy with it why did you call in a pro. I am not a car mechanic I trust my mechanic I do not go on car mechanic web sites. He tells me what's wrong and fixes it. Same as We HVAC pros do with our customers
    You've never heard of a car mechanic inventing problems so that they can charge customers more money? You must have some unusually trustworthy mechanics where you come from, unfortunately around here not every professional is 100% honest, and not every professional is 100% competent (it was a professional that installed this stuff in the first place, remember).

    No, I'm obviously not happy with the system, but my question is whether it is really necessary to replace all three major components of the system to solve this problem.

    Its like Ronald Reagan said: "Trust, but verify".

  8. #8
    Oh, I should add that over the years we've had quite a few professionals from various companies poke around in our attic to see what is wrong with our AC unit (we have these problems every August, but its fine when the outside temperature stays below 95F or so).

    None of them have ever said anything about our ductwork being a problem.

  9. #9
    Join Date
    Feb 2009
    Location
    Portland OR
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    1,942
    Quote Originally Posted by Jimmyhat 597 View Post
    You obviously have problems with the system if you are happy with it why did you call in a pro. I am not a car mechanic I trust my mechanic I do not go on car mechanic web sites. He tells me what's wrong and fixes it. Same as We HVAC pros do with our customers
    Someone sounds a bit like a
    Check out my YouTube channel - http://www.youtube.com/user/skyheating1 We have customer testimonials, product reviews and more!
    Like us on FACEBOOK if you like our advice here!

  10. #10
    Join Date
    Oct 2010
    Location
    SW Michigan, near Battle Creek
    Posts
    921
    every august since when?

    a service guy usualy does what he can do to get the most out of the existing system. And if you call every August in the hottest weather he has more than enough to do.

    it is possible that the system is just undersized and it would make sense to change everything and have it all match.

    the first thing is the ductwork needs to be sufficient.

  11. #11
    Join Date
    May 2006
    Location
    Philadelphia, PA
    Posts
    1,375
    It sounds like you only notice a problem when it is hottest outside. It's time to start with the basics - heat loss / gain calculations, full duct evaluation (Duct Blaster), and look at ways to improve building efficiency. I highly recommend a blower door test to determine infiltration areas. Seal the building. Then look at the HVAC system and determine what needs to be done to make it operate efficiently and reliably. Might be full replacement, might just be a good cleaning and duct modifications.

    I would not be concerned with the mismatched equipment just yet. Without all model numbers I could be wrong, but the equipment as described can be made to work adaquetly.
    Climate Control Solutions for your Home or Office

    Serving Northeast Philadelphia and Surrounding Areas

  12. #12
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    33,916
    Take your time and don't replace anything til someone finds out exactly what is going on. A 21° drop is good IF you have sufficient airflow and you aren't picking up a lot of heat in ducts in an attic.

    Most 50K furnaces have a 3 ton blower so if the duct system is up to snuff, you have the airflow.

    As others have said, post all the model #s you can find to help us sort things out. I've seen "3 ton" outdoor units with "5 ton" coils that were factory called for matches.

  13. #13
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
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    1,070
    Quote Originally Posted by BaldLoonie View Post
    Most 50K furnaces have a 3 ton blower so if the duct system is up to snuff, you have the airflow.
    +1. Do a little more digging to see which model furnace you have. Most furnaces under 90,000 BTU can deliver 1200CFM (which your 3 ton AC needs, nominally).

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