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Thread: Nest 2.0 and Aprilaire 600?

  1. #7
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    Quote Originally Posted by pruitts View Post
    I found the relay at Amazon. I'm sure there are other locations that carry it.
    It wouldn't matter where you connected it but would be easier if connected near the humidifier given the other wires needed.
    Industrial Grade 6AZU2 Enclosed Fan Relay, SPNO, 24V
    Thank you





  2. #8
    HVAC Thermostat Specialist

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    Quote Originally Posted by hvactechfw View Post
    Here is a wiring diagram. You need a relay for it to work properly. I do NOT recommend connecting the humidifier to the hvac 24V power. Follow the diagram and it will work.Attachment 153
    Why do not recommend hooking the solenoid straight to the * and C terminal? I wouldn't think it would draw much power... Industrial Grade Relay

  3. #9
    HVAC Thermostat Specialist

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    The reason why is because if the solenoid or something in the humidifier circuit were to fail or short it would cause the furnace to not work. It is simply a safety precaution and besides that is why humidifiers like the aprilaire 600 come with a transformer; why not use it.


  4. #10
    HVAC Thermostat Specialist

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    Quote Originally Posted by hvactechfw View Post
    The reason why is because if the solenoid or something in the humidifier circuit were to fail or short it would cause the furnace to not work. It is simply a safety precaution and besides that is why humidifiers like the aprilaire 600 come with a transformer; why not use it.
    The odds of a solenoid shorting out are minimal, if somebody is concerned about it blowing the transformer then put a 3A fuse on the transformer secondary if there isn't already one there. Eliminating the extra transformer reduces standby losses. The relay could be wired to cut power to the primary side to eliminate standby losses.

    Having 2 transformers also increases the odds of a homeowner miswiring something and blowing a transformer/board. Keep in mind most people visiting the forum are not HVAC technicians. I've gone behind many installs gone wrong that involved 2 transformers. Wiring diagrams are easy enough to understand but translating it to the wiring on the actual unit is where the problem occurs.

  5. #11
    HVAC Thermostat Specialist

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    I have gone behind many installs done by professionals that did not use a separate transformer for the humidifier and that caused all kinds of problems. You are welcome to your opinion, but mine will not change. I made a simple diagram and when followed it will work. If you want to suggest something different then you are entitled to. Will my way work, YES! If a homeowner does not understand or has a question then that is what this forum is for or they can call a professional.

    Standby loses are VERY, VERY minimal by a 15VA transformer...................so minimal that it is not even worth mentioning...........

    if somebody is concerned about it blowing the transformer then put a 3A fuse on the transformer secondary if there isn't already one there.
    You missed the point. Even if you save the transformer and only blow the fuse then you still won't have heat.

  6. #12
    HVAC Thermostat Specialist

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    So if the humidifier solenoid shorts out it will eat the transformer on the humidifier side, but yes they will still have heat. I'm surprised you have found so many solenoids shorted, I've never seen it. Central humidifiers aren't very common around here anymore. Most of the ones I see were installed in the 80's and abandoned years ago. Only about 1 in 10 that I find are actually working when I see them. Most people don't want to mess with the filters and clean them out.
    Enclosed Relay


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