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  1. #27
    Join Date
    Jul 2007
    Location
    Chicagoland
    Posts
    481
    Check the dryer vent, it's a long shot but who knows?

  2. #28
    Join Date
    Jun 2008
    Posts
    35
    is the unit short cycling? Is the fan set to auto? Is the evap coil clean?

  3. #29
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,775
    Fall came around and it got cool so the humidity problem went away last year. Fast forward to this summer and of course, customer called again. Figured I'd update what I found and what fixed it. The stacks,or lack of, going up into low sidewall registers were all leaking, mastic sealed those, put an attic tent on pull down staircase and raised air handler up to get a better fall on drain. What I believe was happening was the dominant supply leakage was increasing infiltration through the attic hatch and that hot moist air was cooling down to close to dew point temp and raising rh. Also, lowering the fan speed made the air handler/ducts colder increasing the sweating. Once I fixed the other stuff I raised the blower speed back to 400cfm/ton. I think this problem had been ongoing with the old system as well as the new one, but last year the dp, rh, and temps were all making the conditions just right to make all of the problems more noticeable. It was a great learning experience for me. Thanks to all that replied.

    Edit: when we installed the unit we also sealed all the return with mastic and not the supplies which made supply leakage even more dominant.

  4. #30
    Join Date
    Feb 2005
    Posts
    288
    what rh% do you have in house now

  5. #31
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,775
    Quote Originally Posted by joebear View Post
    what rh% do you have in house now
    high 40s to low 50s

  6. #32
    Join Date
    Jun 2013
    Location
    South Caolina
    Posts
    23
    We have the same problem with one of our customers. Got the unit 2 years ago and she never has been real happy with the humidity. We tried everything last year, tomorrow we are downsizing her unit from 3 1/2 tons to 3 tons at our expense. This should fix the problem otherwise she needs better insulation. Its not something we want to do but in a small town sometimes you have to bite the bullet to save from word of mouth.

    Let us know what happens.

  7. #33
    Join Date
    Feb 2005
    Posts
    288
    does a b4vm36 ahu match with a 3.5 ton outdoor unit?

  8. #34
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,775
    Quote Originally Posted by DRC525 View Post
    Let us know what happens.
    I already did, humidity is down, customer is happy. Just took a little investigative work to find the cause. We had already downsized from 4tons to 3 1/2.

  9. #35
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,775
    Quote Originally Posted by joebear View Post
    does a b4vm36 ahu match with a 3.5 ton outdoor unit?
    It may be a 42 or 48 air handler, I don't remember or have the info with me.

  10. #36
    Join Date
    Jun 2013
    Location
    South Caolina
    Posts
    23
    Thanks! Somehow I missed that part, makes me feel better about doing ours tomorrow. The downsizing should help here too.

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