I have a new furnace that did not come with a humidifier and I'd like to put one on - I've done some basic wiring in the past, but it's not my strong suit and I'm a little confused :)

Here's where I'm confused. According to this wiring document for the humidifier, it says to use the 110v -> 24v converter to power the solenoid (bottom right of the left hand diagram):

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However, I've read a lot of articles online that say that some furnaces already have a dedicated 24v connection I could use instead (as long as it's not the blower connection) - does that make sense? The furnace is an Amana AMS81005CXAC, and the hookups are here (thermostat wires come in on the right):

enter image description here

The circuit board says "Emerson Climate Technologies" and has what looks to be an unused/unusable humidifier hookup on the left? I don't have a manual for this board, so I don't know.

The AMS8 manual has only this to say about a 24Vac humidifier: "The yellow wire connected to the ID Blower pressure switch is powered anytime the pressure switch is closed and provides 24VAC humidifier control. Remove the yellow wire and connect a field supplied jumper wire with a piggyback terminal to the pressure switch terminal. [...] Connect the COM side of the humidifier to the C terminal on the furnace control board or to the COM side of the 24VAC transformer."

So I guess where I'm at is:

Do I need to install a 110v outlet (there isn't one on or near the furnace) and use the included 110v -> 24v converter to power the solenoid? Do you see any places where I can hook up the solenoid power on the circuit board instead?


1 Answer 1


For the automatic humidistat, aka what you have

Since you're using the automatic humidity controller, this gets somewhat...interesting. Wire up the R, C, W, and Gf terminals as directed to the furnace terminal block -- you will need to pull the G wire from the thermostat off the terminal block and send it to the G terminal on the auto-humidistat as well. Then, jumper the R terminal from the furnace to one H terminal on the humidity controller, and connect the humidifier valve wires to the other H and the C terminal on the auto-humidistat.

If you were using the manual humidistat

There is a yellow wire going from pin 10 of the 12 pin control board connector to the blower pressure switch i.e. the yellow wire that goes into the pin on that connector closest to the terminal block -- you'll need to tap into that wire and send it off to the humidistat as well as to the blower pressure switch. Your other wire from the humidistat goes to one terminal of the water valve, with the other terminal of the water valve getting spliced into the blue C (Common) wire from the transformer.

In general, a wire tap like that would be done by cutting the wire, crimping a female tab terminal (faston, quick-connect) on one end and a male tab terminal on the other, and then using a female/male tab terminal tap connector to make the 3-way connection. (So called "vampire tap" terminals aren't as reliable as properly made crimps.)

  • You're being so helpful, thanks! Here (i.imgur.com/QVHRWMR.png) is what I think you are describing - the dotted lines are the ones I'm a little unsure of, is that what you meant?
    – James F
    Commented Nov 25, 2016 at 19:40
  • @JamesF -- you're right on the money! Commented Nov 26, 2016 at 1:54
  • Finally got around to wiring it, works perfectly, thanks again!
    – James F
    Commented Dec 3, 2016 at 16:45

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