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Thread: Nest and Humidifier - Relay Question

  1. #1
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    Nest and Humidifier - Relay Question

    Just installed an Aprilaire 600. Bought the 6AZU2 relay as most have suggested on this forum.

    It's all wired, but not working.

    I have 24 volts at pins 1 & 3 (Coil Side) on the relay when the system is running and Nest calls for Humidity.
    But there is no voltage down on Pins 2 & 4, so the humidifier is not getting the signal for water.

    Seems to me the relay is bad. As I understand it, when pins 1 & 3 are energized it CLOSES Pins 2 & 4 providing the connection with 24 Volts.

    The system also includes the 120 - 24v Transformer that came with the Humidifier, and the Solenoid itself, (2 wires) \

    I suppose I could remove the relay, connect * from Nest to one side of the Transformer with one of the Solenoid wires, and connect Common from the system to the other side of the Transformer with the other solenoid wire.

    Honestly I dont know the Transformer is doing, we only have 24 V coming from the Nest and system, I dont see any damage possible to the Solenoid.

    Thanks for any advice.


  2. #2
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    Okay, got it working. Tried a few things with the relay, all failed, but the relay is switching and as I learned, it does not transfer the voltage to the bottom pins, only closes the circuit. It was working correctly, but even after connecting the 24v to one of the solenoid wires I could still not get the solenoid to open.
    I then removed both the Relay and the Transformer that came with the Humidifier. Connected the * from Nest to one of the Solenoid wires and connected the Common from the HVAC board to the other Solenoid wire. Works perfect. Shuts off when Heat shuts off, and turns on with heat, if the Nest is calling for Humidity.

    Figures I would get this thing installed and working on the most Humid day in December ever. Anyway, the wife will be happy, and I will be happy to throw out the noisy humidifier she runs. I call it the Cold Wind Machine. We have an extremely dry house, down to 22% humidity often. We burn a lot of fires in the woodstove, so I will need to humidify the air before and after with the heating system.

    Any comments on that Relay or Transformer on the correct way to use them would still be appreciated.


  3. #3

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    Maybe there is a issue with the contacts on the relay. When the relay clicks the contacts on the relay should close.

  4. #4
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    Click image for larger version. 

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    This is what your wiring should look like. Don't ever run IAQ accessories directly from the equipment transformer, and in the case of the Nest, off the * terminal. If your accessory fails electrically, it may damage the equipment and leave you without heat.

  5. #5
    Junior Member

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    cahilj - what is the component in the bottom left of your drawing? I can easily match the wiring, but I dont have anything adding voltage to for that connection through that component. I can take voltage off of the nest wire and piggy back it down to the bottom of the relay wire. Any thoughts?

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