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Old 05-05-2017, 08:47 PM  
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Default Thermostat HELP! Mercury to Digital


I'm a new home owner and came across my first project. I have an AC system (doesn't seen to work), and a gas furnace for the heater. I purchased a basic digital Honeywell thermostat to replace my mercury one. The wiring doesn't seem to make much sense to me, as I figure I just match the colors accordingly?

One image is the wiring on the mercury thermostat. 1-red, 1-yellow, 1-white, 1-brown? But the part that confuses me is how the yellow wire hooks up to the white terminal. How do I wire for the digital thermostat?


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Old 05-05-2017, 11:21 PM  
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Welcome to the site
It does look like they had the yellow going to the W screw. but that will depend on how things are hooked up in the furnace.
You may want to take a photo of that too so when a pro comes along he will have more info.

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Old 05-06-2017, 06:15 AM  
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I had the same problem with mine going from and old mercury Honeywell to a new one like yours. I don’t remember how mine is now wired as it has been a few years but I remember I called the 800 number and they walked me right thru it. If you don’t get a few replies from a pro soon then you could try that option.

And welcome to the forum. Post back when you get it done.
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Old 05-06-2017, 07:20 AM  
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hook your wires up the same as they are attached at the furnace.
Use the terminal designations (R, B, W, Y, G, etc) at the furnace to match the terminal designations at the thermostat.
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