enter image description hereenter image description hereenter image description hereenter image description hereenter image description hereenter image description hereI've read the related posts, but they don't answer my questions. Please, help!

We had contractors installed: * Aprilaire-700 Humidifier with Auto/Manual Humidistat-Control Knob (non-digital) * York Heating-Furnace Model TG9S080C22MP11 s Serial W1B4453800 - newly installed.

Humidifier has Wires: Yellow, Blue - to 24VAC;
Green - unused to no where;
Red & White - to Humidifier;
Red & White - to Outdoor Temperature Sensor.

The YORK furnace is working fine, new upgrade. The slick contractor left the humidifier wires unconnected back to the new furnace, following replacement.

The Furnace works fine! But: Q1. How do I know which humidistat wires to connect to Furnace Control Board Terminals? Q2, Q3. Exactly which Terminals on the Furnace Control Board - which ones and how?

The children are all getting sick with dry throat, bleeding nose, dry eyes, even getting dizzy & disoriented. Please, HELP! Thanks.

  • Typing in all caps is considered YELLING; what'd I do to deserve that? Anyway, have you thought of calling Mr. Slick back to finish his job? Commented Feb 17, 2015 at 19:24
  • Thanks, Chief. I'd try to edit the text - the caps were for emphasis, not meant to be rude - sorry. Mr. slick wants to charge me a few hundred dollars, just to reconnect the wires. He's been avoiding calls. I can do the wiring, if I know which wires to connect. Any help will be appreciated. Thanks. Commented Feb 17, 2015 at 20:04
  • What are the new images meant to illustrate? Is that artwork you found on the net, or diagrams the installer left?
    – Tester101
    Commented Feb 19, 2015 at 23:28
  • Tester101: Thanks, I explained the new images in my separate comments to your earlier Diagram-responses. Please, see the 2 comments below, far down. The box only accepts a limited number of characters. Perhaps, I can repost them again, next. Commented Feb 20, 2015 at 4:35
  • Re-posted from below:..... { Teater101: Thank you very much for your response, especially taking the trouble to prepare the Schematic Wiring Diagram in the exact wire-colors. I was in the process of connecting the wires based on your diagram, then a another opinion was made.....read next comment. – Osborn Neal 6 hours ago } Commented Feb 20, 2015 at 4:38

2 Answers 2


There's two ways to wire this up. The first method is to take advantage of the HUM terminal on the furnace control board. This terminal will supply 120 volts when the furnace is running in heat mode, so you'll have to use an additional transformer.

Humidifier wiring with transformer

You'll hook the primary side of the transformer to the HUM, and Neutral terminals in the furnace. Then you'll connect the 24VAC terminals of the humidistat, to the secondary of the transformer.

The other method, is to use the furnaces transformer to provide power to the humidistat. However, you'll have to make sure the transformer is large enough to supply the load.

Humidifier wiring without transformer

With this setup, you'll connect the 24VAC terminals of the humidistat to the C and W terminals on the furnace control board. That way when the thermostat calls for heat, the humidistat will be powered by the furnaces transformer.


The yellow and blue wires should be connected to W and C of the control board. You will need to connect them where the thermostat wire is connected. Doing this will give your humidifier/humidistat power when the furnace is in a heating cycle.

  • Mnc123, thanks much for coming to my rescue, here. I've been down in the untility-room for the last hour, taking notes, tracing & labeling the wires, and trying to make sense of the connections, since I received your response. Commented Feb 18, 2015 at 0:45
  • As you see in PHOTO 4, Yellow, White, Green, & Blue wires run from the Furnace Terminals (left, bottom corner of Board). Are these the terminals you refer to? I noted that: (1) Yellow & Blue wires from the Furnace Terminals, Outside-Wire, & Upstairs Thermostat - all connect together. (2) Green, Red, & White wires from Furnace-Terminals & Upstairs-Thermostat connect together. Continued, in next comment.... Commented Feb 18, 2015 at 1:25
  • QUESTION 1 - So, as I understand your suggestion, I should connect the Yellow & Blue Humidistat wires to the Furnace-Terminals where the Yellow & Blue Thermostat/Outside wires are already connected - correct? That would leave me with Red, White, & Green Humidistat wires. So, QUESTION 2 - Connect the Red & White Humidistat wires to the 2 wires coming from the Humidifier - Correct ? Continued, next comment... Commented Feb 18, 2015 at 1:27
  • Please, pardon me for these long narrative, I just want to make sure I make sense of the wires and follow your suggestions. You've given me som hope, and i hope to get the Humidifier running - if I can get your reply, tonight. Thanks, again - I look forward to your reply. - Osborn Commented Feb 18, 2015 at 1:29
  • I was under the impression that the humidifier was already wired as well. I assume this is not a new humidifier. And also does it have a digital controller? And yes the red and white should go to the 2 wires coming off the humidifier solenoid
    – Mnc123
    Commented Feb 18, 2015 at 2:50

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