Honeywell RTH9580WF install help- C Wire problems


Old 04-05-15, 05:36 PM
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Honeywell RTH9580WF install help- C Wire problems

Good evening all,

I'm a bit stumped on the install for this thermostat. I am in the process of replacing my existing thermostat, however have run into a bit of a pickle with the lack of a C wire. The unit I am replacing is a 4 wire unit with no C. Just G, Y, W, R.

Now typically I would just Add a c-wire and run it to the furnace and add it to its respective location on the board. However, there is not the typically strip of screw style terminals. Just three spade style with only G, W, R. There is a screw style terminal labeled 24V HUM next to them, can i use this as my power source for the thermostat?

Im completely stumped and have attached a couple of photos of the board. Any help would be appreciated. I have looked everywhere and do not have an actual wiring diagram. It is a Janitrol unit if it helps at all. I have only been in the house for about three months and was really only replacing because the existing one stopped working all together...Name:  photo 2.jpg
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Old 04-05-15, 05:41 PM
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Welcome to the forums.

I'll need a full picture of the entire board or the part number off that board. The picture needs to be as large as possible to be effective.
Old 04-05-15, 06:25 PM
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Here hope this helps. I attached a photo of the bundle of wires coming FROM the thermostat. You can see there is no blue wire going to anything. They just snipped it all together. But also cut and attached wire nuts going somewhere. Let me know what you think.Name:  photo 1-1.jpg
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Old 04-05-15, 06:36 PM
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The wire that connects to the furnace body is "C" (24 volt common).
Old 04-05-15, 08:38 PM
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I had a feeling just based on the switch for the door sensor is run to that screw so it has to allow power to something i.e everything.

Worked perfectly. Thanks guys!
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