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Thread: Trane A/C System Capacity Reduction

  1. #1
    DIY Junior Member offsit123's Avatar
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    Default Trane A/C System Capacity Reduction

    My five year old Trane HVAC system includes an XV90 (UY100R9V4w) with a 5 ton Condenser (2TTB0060A) and coil (2TXCC060AC3HCA).

    It is oversized for my home. The A/C short cycles and humidity is not well controlled.

    Also, the ducts are too small for even the lowest A/C airflow setting and there is quite a roar from turbulence in the return air duct and thru the grill.

    I would like to reduce the A/C to a 3 ton capacity (which is adequate for our mild climate).

    Two questions, please:

    1) Can a new 3 ton condenser work with the 5 ton coil I have now (guessing no)?

    2) If I swap the existing 5 ton single stage condenser for a 5 ton two stage unit (Xl16i), will that work with the existing 5 ton coil?

    Thanks!

    -Tom-
    Last edited by offsit123; 12-07-2011 at 09:43 PM.

  2. #2
    Plumber jimbo's Avatar
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    It would not be unheard of to have a condensing unit 1/2 ton smaller than the coil. I think 2 tons smaller is out of the question.
    You would have to ask Trane if the two stage unit would work on that specific coil, or with the blower set up in your furnace. You might need a different thermostat also.
    A new 3 ton coil would be a minor expense compared to the condensing unit. As far as I know, Trane is not doing dry 22's, so if you are not already on an R410 unit, the cost to flush your system would be almost as much as just getting a new 3 ton coil to go with the R410 condensing unit. I am pretty sure the 2TTB is an R22 unit.

  3. #3
    Jack of all trades DonL's Avatar
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    You may want to check SW-2 #5 and #6 to verify that they are both ON, if you have not yet done so. That unit should have a Variable Speed Blower Controlled by SW2.

    With #5 and #6 in the ON setting, that puts the unit into ENHANCED MODE, for better Dehumidify and Efficiency.

    That setting controls the Blower Ramping, For the AC, and should reduce the Blower Motor speed.

    That would not fix your BTU rating but JimboŽ is correct about that big of a jump, and the coolant.

    Did it take 5 Years to figure out it was oversize ?
    Last edited by DonL; 12-09-2011 at 11:56 AM.
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    DIY Junior Member Offsite's Avatar
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    Thanks, DonL,

    Yes, the switches are set to ramp the AC fan speed... but only ramps for a short while and then full speed. Also set the full speed down to the minimum that would avoid coil freezing up.

    We were living with the 'oversize' issue up to now because, here in SoCal, AC is not used that much. But a recent 'water adventure' ended in removing the HVAC unit from the furnace room, so "why not correct the issue now that the whole system is out on the deck?", was our thinking...

    Btw, I spent a miserable 'year' in Houston, over a seven day period awhile back trying to get an instrument qual'd for flight... so I know the environment there would have demanded a more timely response to an oversized AC system...

    Thanks for the reply.

    -rb-
    Last edited by Offsite; 12-09-2011 at 12:51 PM.

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    DIY Junior Member Offsite's Avatar
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    Hi Jimbo,

    As usual, good and practical advice!

    Guess I'll swap the coil too, since you are correct that this is an R22 system.

    Btw, giving up on the Hydronic concept... again, you were right... it didn't pencil out in our environment.

    Thanks, again, Jimbo.

    -rb-

  6. #6
    Jack of all trades DonL's Avatar
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    Quote Originally Posted by Offsite View Post
    Thanks, DonL,
    Btw, I spent a miserable 'year' in Houston, over a seven day period awhile back trying to get an instrument qual'd for flight... so I know the environment there would have demanded a more timely response to an oversized AC system...
    -rb-
    Sorry You had to Suffer Houston Humidity and Weather.

    I worked for NasaŽ installing and working on Heads Up instruments and displays, and some other systems.

    I wish I had your problem, Because Houston weather sucks and I could use a few more BTUs.

    Want to trade AC units ? lol.

    I miss the days working at Edwards Air Force Base.


    Sounds like you may be better off replacing your unit, If it is really a problem.


    Good Luck on your project.
    Last edited by DonL; 12-09-2011 at 01:04 PM.
    Theory only works perfect in a vacuum.

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    DIY Junior Member Offsite's Avatar
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    Thanks, DonL,

    I'll definitely report back after things settle out...

    73
    -rb-
    PS: Edwards is a cool place... had cert training there in prep for some zero-g work at Wright-Patterson several lifetimes ago. Heads Up is an amazing technology, btw, I can only imagine what it's like to fly all the new stuff...

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    DIY Junior Member tray's Avatar
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    I see you've had plenty of responses,and yes all of your problems are resulting from improper sizing at all levels.Remember to have 5ton equipment you need house large enough plus properly sized ducts to accomadate this volume of air. A rough rule of thumb is 1ton of cooling per 1,000sq.ft of house. This is a again ballpark figure, you need to also calculate heat loss/heat gain.You very well could have a 2,200sq.ft house that appears to take 2.5 tons of AC, but how many windows? Do those windows have the rating to minimize the suns ability to raise house temp which might move you up 0.5-1 ton. The best way i have found to help my hvac customers in the northeast, is to have an energy audit. This is something my company does for free, it will properly size your hvac equip, and inform you on other ways to improve comfort. Shop around ,ask questions( part/labor warranty ,company refrences and if there is workmanship guarentee). Trane is a great product but make sure you have a need for a two stage condenser. Having a properly sized unit is first step( and will make huge diffrence and two is condensers having "ecm" motors are starting to be more common and will modulate themselves depending on demand

  9. #9
    DIY Junior Member Offsite's Avatar
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    Thanks for the reply, tray... it helps us see we are on the right track.

    We bought this 2nd floor unit new in 2006. The 5 ton HVAC system was already in place. The builder used the same 5 ton spec in all units. It was probably needed for the 3rd (top) floor units (2500 ft-sq) because they have maximum sun exposure and the roof is above them.

    For our 2nd floor unit (2000 ft-sq), with its very limited sun exposure, excellent wall insulation, and double pane glass in all windows, 3 tons should be adequate. It is also the minimum we could downgrade to and keep the existing 'air handler'.

    We've decided to go with the Trane 15i (single stage) roof unit. The max air flow rate will be about half of what it was for the 5 ton system we are replacing. That should help control the RH a bit, as well.

    We could have kept the same coil, but, after reading the wise advice given in this thread, we decided to go with a new one that is designed to work with the new condenser and its different refrigerant.

    We are starting this project hopefully next week, so we will report back after things stabilize.

    Thanks to all for your thoughtful replies!

    -rb-

    Quote Originally Posted by tray View Post
    I see you've had plenty of responses,and yes all of your problems are resulting from improper sizing at all levels.Remember to have 5ton equipment you need house large enough plus properly sized ducts to accomadate this volume of air. A rough rule of thumb is 1ton of cooling per 1,000sq.ft of house. This is a again ballpark figure, you need to also calculate heat loss/heat gain.You very well could have a 2,200sq.ft house that appears to take 2.5 tons of AC, but how many windows? Do those windows have the rating to minimize the suns ability to raise house temp which might move you up 0.5-1 ton. The best way i have found to help my hvac customers in the northeast, is to have an energy audit. This is something my company does for free, it will properly size your hvac equip, and inform you on other ways to improve comfort. Shop around ,ask questions( part/labor warranty ,company refrences and if there is workmanship guarentee). Trane is a great product but make sure you have a need for a two stage condenser. Having a properly sized unit is first step( and will make huge diffrence and two is condensers having "ecm" motors are starting to be more common and will modulate themselves depending on demand

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