Question about Aprilaire 700 Humidifier

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Water runs when furnace is off, but stops when furnace is on.

We just moved into this house, and it had the Aprilaire 760 installed, but disconnected. When I put it back together and turned the water on, the water kicks on when the furnace is off and the humidstat is turned up. When the furnace comes back on, the water cuts off. It's clearly wired backwards, but I can't figure out what's wrong.

There is a 24V transformer near the humidstat, and one of the feeds runs through it. It has constant power being fed to it. The plug for the humidifier is plugged in to an outlet on the furnace that only has power when the furnace is running. The brown wires coming off the humidifier are wired to the humidstat (one of which has the 24V feed).

Hopefully that gives enough detail to help.

Thanks!

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  • sheff528 Jan 30, 2009

    You nailed it! I hooked up the leads from the humidstat to bypass the transformer, and everything worked great! My humidity has come up a couple of % points to 27%, so we're headed in the right direction.



    One question, though. I noticed water runoff through the drain while the furnace was on. Is that normal? It wasn't a whole lot, but seemed more than I expected.

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The 760 humidifier does not need a transformer wired externally. the 760 has its' own 24v transformer inside the fan compartment. this transformer will provide the power to enrgize the water solenoid as needed. it sounds like to me the additional trasnformer is hot all the time. when the furnace comes on, the unit gets power and the internal transformer is cancelling the power from the external transformer. this would explain why it quits running when the heat is on. since the external transformer is hot all time, when the heat shuts off, the solenoid is getting energized by the external transformer. to make this run correctly, you need to get rid of the external transformer. leave the humidifier high voltage wires hooked up so they are only hot when the furnace runs. if you have a humidistat that has a r and c terminal, you will need to wire these directly to the r and c on the furnace control board and move the switch inside the humidistat to "power". make sure it is not on "bypass". then wire your 2 brown wires from the humidifier to each of the "h" terminals on the humidistat. if you have a humidistat that only has 2 terminals, wire one brown wire to each of the terminals. this should allow it to run properly.

Posted on Jan 28, 2009

  • brian baldwin Jan 30, 2009

    that is one of the drawbacks of this type of humidifier. you will have water go down the drain and not into the air. there is an orifice on the inlet side of the water solenid tubing that controls the flow rate.

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