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  1. #1

    Honeywell IAQ Dehumidify Question

    I have read various posts of people with similar problems but I cannot get my IAQ to succsessfully use my A/C to dehumidify. I have ...

    Furnace: Carrier 58PAV135-20 series 151 (single stage)
    A/C: Carrier 38CKB060300 (single stage)
    Humid: April Aire 600 [currently not connected in order to simplify setup pending resolution of dehumid problem]

    First off, I have no experience wiring this level of complexity tstat, but with such a basic setup, I figured there would be little problem.


    My IAQ is set to fan(auto) and system(auto) with dehumid set to 45%. The heat temp is set to 65 and cool to 77. The current indoor humidity has been between 60-70% all day and the A/C will kick in reducing the indoor temp to 3 degrees below the cool setpoint (as per setup function 0383 I assume) but will not continue cooling to reduce the humidity.

    What strikes me as odd is that on the dehumid screen, the AUTO/OFF option is present ... even though setup function 0379 (dehumid control) is set to 1 (dehumid with AC). The Operating Manual (p18) specifically indicates that AUTO/OFF option is only present when using a whole house dehumid and is not present when dehumidifying with the AC.

    For clarity, I have the AC wired to Com and Y only, not DHM.

    Any and all help is greatly appreciated.
    Todd

  2. #2
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,707
    diy not allowed here.......

  3. #3
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    You need some modifications to your unit.
    The IAQ will run your system to cool, but since you don't have a VS blower for it to slow down, it won't be able to actually dehimidify.

    Any competent contractor, can easily make teh alterations for you.
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  4. #4
    Allow me to clarify DIY-"appearing" thread:

    I just bought this house about two months ago. The sellers provided proof of "maintenance check" of HVAC system as condition of sale. Now that the deal is done, I have noticed the peculiarity described. I have contacted the company that performed the maintenance check and they will come out to check my concerns ... for $75. Before I invest this money, I want to know if I have a legit concern or if a simple incorrect setting was originally missed.

  5. #5
    Join Date
    Feb 2003
    Location
    garland, texas
    Posts
    663
    A maintaince check to the person selling the home my only mean change the filter, clean the condenser, blow out the drain, and verify there is some refrigerant in the system, I do not want to spend anymore money on this house I'm selling it. A maintaince check is usually interpreted by the home buyer to mean the a/c is correctly sized for the house, everything is running like a fine swiss watch and my utility bills will very low.

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,266
    Quote Originally Posted by Todd546 View Post
    I have read various posts of people with similar problems but I cannot get my IAQ to succsessfully use my A/C to dehumidify. I have ...

    Furnace: Carrier 58PAV135-20 series 151 (single stage)
    A/C: Carrier 38CKB060300 (single stage)
    Humid: April Aire 600 [currently not connected in order to simplify setup pending resolution of dehumid problem]

    First off, I have no experience wiring this level of complexity tstat, but with such a basic setup, I figured there would be little problem.


    My IAQ is set to fan(auto) and system(auto) with dehumid set to 45%. The heat temp is set to 65 and cool to 77. The current indoor humidity has been between 60-70% all day and the A/C will kick in reducing the indoor temp to 3 degrees below the cool setpoint (as per setup function 0383 I assume) but will not continue cooling to reduce the humidity.

    What strikes me as odd is that on the dehumid screen, the AUTO/OFF option is present ... even though setup function 0379 (dehumid control) is set to 1 (dehumid with AC). The Operating Manual (p18) specifically indicates that AUTO/OFF option is only present when using a whole house dehumid and is not present when dehumidifying with the AC.

    For clarity, I have the AC wired to Com and Y only, not DHM.

    Any and all help is greatly appreciated.
    Todd
    Without getting into the detail of equipment, here are a couple suggestions. Over cooling 3^F is the t-stats simple way of dehumidifing. The basics of maxing the moisture removal of the a/c is slow the air flow over the cooling coil to all the coil to get cold enough. Coil temps of 45-50 remove more moisture. The limitations are coil freeze-up and sweating ducts. Typically, you need enough cooling load to remove 5-8 gals. of moisture per day to maintain <50%RH. A 3 ton a/c removes a gallon of moisture per hour. 5-8 hours of cooling is needed at a minimum to maintain <50%RH. Cooling to 78^F with a 3^F over-cool for dehumidification will not get you to <50%RH during wet cool weather.
    Using a whole house dehumidifier like the Ultra-Aire will get you <50%RH during low/no cooling load conditions. These units are added to your a/c. The dehu with a well tuned a/c will provide any temp/%rh combination you want. Check my posts for more discussion. Regard TB
    PS I use a system similar to yours and have posted data.
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  7. #7
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Why do you have the IAQ on a very basic single stage non-variable speed furnace.

  8. #8
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,750
    Maybe he plans to get a VS furnace later.
    And doesn't want to pay for a stat twice?
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  9. #9
    Join Date
    Dec 2006
    Location
    Middle Tennessee
    Posts
    11,347

    *

    Quote Originally Posted by mayguy View Post
    Why do you have the IAQ on a very basic single stage non-variable speed furnace.
    even with a multi-speed non variable speed furnace;

    a standard relay can be used in conjunction with the IAQ to lower the fan speed on a call for dehumidification!



    .

  10. #10
    Join Date
    Dec 2002
    Location
    Rochester, MN
    Posts
    5,304
    Quote Originally Posted by Airmechanical View Post
    even with a multi-speed non variable speed furnace;

    a standard relay can be used in conjunction with the IAQ to lower the fan speed on a call for dehumidification!
    True, and hope the coil has a TXV on it.

  11. #11
    Join Date
    Jul 2008
    Posts
    551
    What role does the TXV play in this? What about the TXV helps dehum?

  12. #12
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,707
    Quote Originally Posted by badtlc View Post
    What role does the TXV play in this? What about the TXV helps dehum?

    txv will help prevent turning the evap coil into a block of ice if you slow down the indoor blower to dehumidify.

  13. #13
    Join Date
    Jul 2008
    Posts
    551
    Quote Originally Posted by t527ed View Post
    txv will help prevent turning the evap coil into a block of ice if you slow down the indoor blower to dehumidify.
    I assumed that from his response. I'm asking how the TXV physically does it. What properties of the TXV provide that assistance?

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