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  1. #1

    New Lennox system

    Hello, I have a question regarding a new Lennox split system
    system info:
    Condensor:XC21-048-230-08
    Furnace:SL280UH090V60C-03
    Coil:CH33-50/60C-2P-3

    Do these components match?
    I believe the condensor is 4ton and the coil is 5ton

    I think the system is oversized due to short run times even when OAT is near 100^. Manual J suggested 3.79ton
    This is a 1650sf type five construction single story residence built in 1996 in Tucson, AZ
    Insulation in the attic is not great, double pane windows are in ok shape.

    All ductowrk is flex, 20 inch return trunk, 20x30 return grill

    thank you for your feedback

  2. #2
    Join Date
    May 2012
    Location
    San Diego, CA
    Posts
    352
    If manual J was done right and suggested a 3.79 ton then your 4 ton system is fine. I usually don't oversize coils, but I know some do to get higher efficiency. So the coil should be fine.

    Is the unit running for at least 15 minutes? How is the temperature in the house? Does it feel comfortable or humid?
    You can call me Sam

    It should be a crime to be a mechanical engineer in San Diego
    Summer Design Temperature: 83 F Dry Bulb ~ 69 F Wet Bulb (California Climate Zone 7)

  3. #3
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,455
    I would have went with 3.5 tons, man j input numbers are a lot of times educated guesses and most err on the overkill side.

  4. #4
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,754
    good match, 49,000 btu's and around 17.50 seer.

    with load calc you gave it is sized properly, make sure it is wired and set up properly so it is going into low stage. also make sure blower settings were adjusted for the 4 ton unit and not left on the 5 ton factory settings.

  5. #5
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,455
    Didn't realize it was 2 stage, make sure it is wired for 2 stage, lots of guys don't because they don't want to pull a new wire

  6. #6
    I can see in the diagnostics on the Icomfort that it does operate a lot of the time at 70% on the condensor, which is low stage.
    Temp in the house feels ok, Rh @ around 35-38% per the stat.

    What should the CFM settings be for a 4ton. Manual J stated house CFM needed was around 1400 as I read it.

  7. #7
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,455
    1400-1600 cfm for 4 tons

  8. #8
    Ok, first stage is set for 1000 CFM and second stage is set for 1500 CFM.
    It seems to do most of its work in first stage, day and night but it definitely doesn't run for fifteen or twenty minutes unless it's really hot outside, like over 100 degrees.
    Also, when the condensor kicks on it makes my lights dim slightly. Just ever so slightly. HVAC company didn't think it was a big deal. Old unit never did it but it was smaller and much older technology. I understand all mechanical devices are different.

  9. #9
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,754
    have you verified the information used to figure the manual j?

    numbers may have been fudged to fit the unit....

  10. #10
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,320
    Old unit was a smaller tonnage? Or just physically smaller?
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  11. #11
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,455
    Quote Originally Posted by Fireferg73 View Post
    Ok, first stage is set for 1000 CFM and second stage is set for 1500 CFM.
    It seems to do most of its work in first stage, day and night but it definitely doesn't run for fifteen or twenty minutes unless it's really hot outside, like over 100 degrees.
    Also, when the condensor kicks on it makes my lights dim slightly. Just ever so slightly. HVAC company didn't think it was a big deal. Old unit never did it but it was smaller and much older technology. I understand all mechanical devices are different.
    Sounds like it is grossly oversized and even the first stage capacity is way oversized, good thing you live a dry climate or humidity would be a big issue for you in the summer.

  12. #12
    Old unit was 3.5tons, single stage Rheem 10 Seer coupled with a single speed furnace.
    And yes, I agree I need to confirm the J calculations.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,320
    First stage has a capacity between 2.8 and 3.2 tons. So in first stage, its almost as much capacity as your old unit. Its probably the VS blower that can move the air better then your old blower could, that helps it to cool your house better in first stage then your single stage 3.5 ton could.
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