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Thread: R-G fan drive

  1. #1
    Join Date
    Feb 2005
    Posts
    5

    Question

    Looking for tech info on Tstat/furnace connections. If I put an external set of contacts across R & G to drive the fan independent of a call for heat, will I somehow be forcing the compressor to run? (Fan switch is in AUTO position.) Or is this possibly Yes, possibly NO depending on one Tstat to the next? Found some literature that seems to suggest this, but need some schematic info to show me why this is.

  2. #2
    Join Date
    Nov 2001
    Posts
    1,874
    Your back feeding voltage through the t-stat subbase to the "y" circuit.
    The "y" circuit energizes the A/C mode.

    If you put the Stat in the "fan on" mode, your stat by-passes the "y" circuit by itself.
    If you try to fail, and succeed.
    Which have you done ?



  3. #3
    Join Date
    Feb 2005
    Posts
    5
    So I'd have to disconnect Y if I want to leave the fan switch in AUTO?

  4. #4
    Join Date
    Nov 2001
    Posts
    1,874
    Yes or the "g"

    remove either one and jumper the "r to g" at the furnace,
    and the blower will run.

    What are you trying to accomplish ?
    If you try to fail, and succeed.
    Which have you done ?



  5. #5
    Join Date
    Nov 2004
    Posts
    240
    Use a spdt relay at the unit to close r-g at the unit and open the g signal from tstat to unit.

    [Edited by djken on 02-16-2005 at 12:22 PM]

  6. #6
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Originally posted by Toolpusher
    Yes or the "g"


    What are you trying to accomplish ?


    He's an engineer with time on his hands. An awful situation.

  7. #7
    Join Date
    Feb 2005
    Posts
    5
    I want to be able to run a humidifier even if there's not a call for heat.

  8. #8
    Join Date
    Nov 2001
    Posts
    1,874
    All you have to do is install a transformer, Line side of transformer to line side of furnace.

    Load side or low voltage side of transformer. 1 wire goes to 1 wire on humidistat, other humidistat wire goes to solinoid valve on humidifer, other solinoid wire goes to low voltage side of transformer. Completing the circuit.

    You don't want to disturbe the fan circuit control wires.

    If you run the humidifier during no call for heat, what are you hopeing to achieve ?
    If you try to fail, and succeed.
    Which have you done ?



  9. #9
    Join Date
    Feb 2005
    Posts
    5
    If I understand you correctly that will open the solenoid valve when the humidistat contacts close. That might be OK for a wet-pad type humidifier, but I'm working with a steam type humidifier, which will generate however much moisture it's told to generate, regardless of ambient temp or RH. I just need to make sure the fan is running when it's making steam.

    I still want the Tstat to be able to turn on the fan as usual too, so it looks like the best approach would be to disconnect the Y terminal during the heating season.

  10. #10
    Join Date
    Jan 2005
    Posts
    113
    I find the only time its worth yor wild to run the fan without the heat is with steam humidifers skuttle #60 etc.just kinda shooting yourself in the foot with a bypass humidifer aprilair etc. they work better with heat on.than off.only downfall tosteam it will rust your duct-work....but is worth it.

  11. #11
    Join Date
    Nov 2001
    Posts
    1,874
    What a long way around robinhoods barn just to reach the front door,

    Meaning, If you would say what your trying to achieve the first post.
    You would have gotten answere without the back and forth part.
    If you try to fail, and succeed.
    Which have you done ?



  12. #12
    Join Date
    Feb 2005
    Posts
    5
    I'm not interested in discussing the pros and cons of humidification, which is why I specifically left that out of my first post. What I AM interested in is what happens when you put a second set of contacts in parallel across R & G, which is exactly what I DID ask in my first post.

    Thanks anyway.

  13. #13
    Join Date
    Feb 2004
    Posts
    2,597
    make sure high voltage of humidifier is wired constant hot.

    use a current sensing relay on blower common wire to humidistat.

    turn fan to "on" at stat.

    problem solved.

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