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Thread: Questions on digital thermostat breakout wiring for fan operation

  1. #1
    Join Date
    Aug 2017
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    18

    Default Questions on digital thermostat breakout wiring for fan operation

    I have a digital thermostat that seems to work fine controlling the pellet stove.

    I would now like it to turn a fan on and off.

    I see that the general instructions for this is to attach the fan wire to the G terminal in the digital thermostat and this is supposed to turn the fan on and off in auto setting.

    I'm no electrical maven so this confuses me - doesn't an electric motor or even a relay require two (2) wires to work - a negative and positive? So why are the instructions only stating to provide a connection of 1 wire to 1 terminal?

    If this is a relay type of setup, can someone please explain to me now what? After I have attached 1 relay wire to the G terminal.

    I have a photo of the terminals in the Lux TX 9000a digital thermostat and the manual for it as well.

    Thank you.

  2. #2
    Join Date
    Feb 2012
    Location
    Lala land, OH
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    234

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    R is your other wire.. It's the "common" If you are adding your own relay, the coil should be rated for 24VAC which is the norm for your every day residential forced air HVAC system. If your stove runs on something different, the relay should match. Some newer thermostats do get power from the control wires and they will care what it is being fed. Those require a "C" wire.

    The diagram is not 100% accurate. The circles for heat, ac and fan should be relay coils.


    Questions on digital thermostat breakout wiring for fan operation-basic-thermostat-wiring-diagram-jpg
    Last edited by Mr T; 08-12-2017 at 05:14 PM.

  3. #3
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    Aug 2017
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    Ah! Okay! Hours researching on the internet and you solved this for me - so much for the intelligence of Google!!

    So if I'm reading your diagram correctly, there is currently a wire running from the R to the 24 VAC transformer (which indeed there is) and the reason the pellet stove comes on at a set temperature is because the Rh wire goes to the relay in the pellet stove and the R is shared among them all.

    So then I would just replicate the above but with a fan instead - G goes to the relay for the fan and the other side of the that relay connection goes to the shared wire that the pellet stove currently uses and which is attached to the transformer.

    Thanks for clearing that up for me and get back if my analysis is incorrect.

  4. #4
    Join Date
    Feb 2012
    Location
    Lala land, OH
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    234

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    In your setup R and Rh are the same wire. Some systems may have a separate transformer for the AC. In that case you'd have a Rh and a Rc but likely no R wire. Some thermostats have a jumper in them connecting Rh and Rc to form R. It wont matter in your case.

    Sounds like you are on the right track.

  5. #5
    Join Date
    Feb 2012
    Location
    Kent, WA
    Posts
    208

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    Just to clarify. The "other" wire to complete the circuit is the black one at the transformer. It is called "common" or perhaps "C". Usually, all the relays are located next to the transformer and this common wire goes to everything using the 24V controls except the thermostat (most thermostats don't need the common wire). The red wire is the power source. It goes to the thermostat and can come out at least of 3 terminals - W (call for heat), Y (call for cooling), and G (call for fan). These are all just a switched version of the red wire. That switched wire (W, Y, or G) goes to its corresponding relay coil. The other end of the relay coil is that common black one mentioned at the beginning (and in reality it may not be black -- there seems to be multiple standards for this "common" wire including brown).

    I'm not sure where you transformer is -- is it part of the pellet stove, or something separate.
    Mark
    Kent, WA

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