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  1. #1

    Humidistat Wiring help needed

    Home is in SW Florida when I'm away for the summer. I wired my humidistat in series with my thermostat, when the temperture set point is met my fan comes on even though the humidistat set point is not. Here is how it's wired,

    The outside unit is a heat pump, thermostat Aprilaire #8465
    24v wired to RC/R and C
    G wired to fan
    Y to one side of humidistat the other side to the compressor (series)
    W to aux. heat
    o/b to reversing valve

    My thinking is moving the G (fan) wire to the Y terminal would only let the fan come on with the compressor when both thermostat and humidistat set points are met instead of only the thermostat's set point. Will this work or is there a better way? Thanks for any help.

  2. #2
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    What is it you are trying to accomplish with your set-up?

  3. #3
    Having the A/C being controled by the dehumidistat when away for the summer. I've been told this is common in the SW florida area.
    Last edited by dan7uk; 12-04-2011 at 07:20 PM.

  4. #4
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    Well, there are humidistats, and dehumidistats. Each serves an obvious purpose. I assume dehumidification is more important than temperature control, as you mentioned you are away for the summer.

    What is the square footage of the home? I would recommend using a whole house dehumidifier controlled by a dehumidistat set at 50%RH, and setting the thermostat to maintain 80 degrees.

  5. #5
    Sorry, I meant dehumidistat.

  6. #6
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    You need to break the R circuit, not the Y circuit.
    Quote Originally Posted by k-fridge View Post
    The laws of physics know no brand names.

  7. #7
    Thanks for you reply Dave, OK I break one side of 24v with the dehumidistat. My thermostat has a battery backup, do I need to remove the batteries to keep the system from running when the dehumidistat not calling?
    Last edited by dan7uk; 12-04-2011 at 08:50 PM.

  8. #8
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    Nope, you're good to go!
    Quote Originally Posted by k-fridge View Post
    The laws of physics know no brand names.

  9. #9
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    Quote Originally Posted by SoFlaDave View Post
    You need to break the R circuit, not the Y circuit.
    I figured since this thread ran its course, it would be OK to continue the topic in a different direction.

    This is commonly done in your neck of the woods? So the Dstat is in series with the Tstat, in an indirect way. Tstat and Dstat have to 'make', to operate the A/C. Interesting.

    What does this do with the temperature swing in the space? What are the benefits, drawbacks to this type of control? I assume this is only for unoccupied operation. Not objecting here.... Just curious.

  10. #10
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    Rather than mess with fancy wiring... they make thermostats that measure humidity and do what you're trying ot accomplish. Cycle the AC based on a RH setpoint. Most will overcool up to 3F (user adjustable) to mainting a RH range.

    I have mine set-up this way. I intentionally keep it about 1F warmer and let it overcool up to 2F if neded when the humidity rises. That way I'm maintining a constant comfort level. Of course it also slows the blower to increase dehumidification.

  11. #11
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    Quote Originally Posted by thermojohn View Post
    I figured since this thread ran its course, it would be OK to continue the topic in a different direction.

    This is commonly done in your neck of the woods? So the Dstat is in series with the Tstat, in an indirect way. Tstat and Dstat have to 'make', to operate the A/C. Interesting.

    What does this do with the temperature swing in the space? What are the benefits, drawbacks to this type of control? I assume this is only for unoccupied operation. Not objecting here.... Just curious.
    They are EVERYWHERE down here with the seasonal residents. Basically when the space is occupied the DH is set to close at anything greater than 10%Rh so its essentially disabled and the tstat can operate normally.

    When they leave for the summer I typically recommend they set the DH at 65% max. Leave the tstat set at 75 to ensure its calling when the DH is and it will tend to keep the house dry with relatively minmal run time. The tstat becomes the slave and generally the temp hovers around 80*
    Quote Originally Posted by k-fridge View Post
    The laws of physics know no brand names.

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