Can someone help me understand my thermostat wiring?


Old 08-18-13, 11:25 AM
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Can someone help me understand my thermostat wiring?

Hi guys,

I'm planning on installing the Nest 2nd gen. thermostat. I removed my old one, however, I don't understand how it has been wired. The colour of the wires don't correspond to the lettering they have been connected to (please see picture).

So my question is, why is it wired this way? Furthermore, should I just wire it the same way with the Nest thermostat?

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Old 08-18-13, 01:13 PM
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It's a shame when someone doesn't wire up the thermostat using the proper color wires, however it doesn't really matter what the color of the wire insulation is, as long as it's wired correctly and you know what the correct colors are.

Assuming that your current thermostat is working correctly, just make a note of which color wire goes to which terminal. If there's room (and it looks like there is), you could tag each wire with the correct terminal color. This will make it easier should you ever lose your color conversion chart.

Yes, wire up the new thermostat the way your current one is.
Old 08-18-13, 01:21 PM
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Welcome to the forums.

Your thermostat was originally setup for heat only. They ran a two wire cable (white and black) that was just enough to run the heat. Someone added central air and the contractor ran a piece of 22 gauge four conductor phone wire.

It would be proper to replace that with the correct cable. Usually the nest requires a Common wire which you don't have now.

Name:  mm.jpg
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Your current wiring is:
R = white
W = black
G = green + yellow
Y = red + black
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