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I have an old Honeywell Q674 thermostat with mercury in the house we just moved into.

I'm attempting to upgrade to the nest 3rd generation thermostat, however the wiring labels are VERY different. I believe I have figured out that:

  • W2=w1
  • G=G
  • O=OB
  • Y=Y1
  • E=aux
  • X=C
  • R=RH or RC

Does there need to be a jumper from rh to 3rd? Does W2 go to W1?

Amy I do would be helpful. Here are some photos.

  • Focus on actual functions moreso than names or colors. – Harper Jul 31 '17 at 22:17
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I just went through this replacing an old stat with a new smart ecobee. It was a pain, but I figured it out with some help online. One tip, check the compatibility test online, there you tell them what wires you have and it will tell you if you're good, or what you need to do.

In my case, I had to actually connect a C wire to my furnace so I could get continuous power to the stat. What I learned was the stat wires are less important than what is actually attached on the board at the furnace.

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