What kind of system do you have?
Is it a Heat Pump? Or a Nat gas furnace with AC?
You need to use one of the extra wires as a C wire and connect it to the furnace C terminal screw.
I suggest you go to the furnace and remove the cover.
Locate the terminal screws where the thermostat wires connect.
I would fix the strange wire colors they used and put the White wire on furnace W
Put the Blue wire on furnace C common (or if it is a Trane they call it B)
Then go back to the Nest and put
Red in RC
White in W1
Blue in C
G in G
Y in Y
Thanks Houptee. I checked the white wire just hanging there and it has 12 mV power from the multimeter. I’m wondering if it was installed without the white wire since the thermostat runs off battery- not sure why. I’m still looking for the terminal near the furnace to confirm the wiring
If it is getting good power when you do the power test and you get good readings it should be ok.
But connecting a C wire is always the best thing to do on these smart thermostats.
You just remove the front cover on the furnace and you will see the wires and screws in a row R Y G C W etc etc.
If you want to make it standardized to the normal color code you can move white to W and blue to C.
This video shows you how to test if you need to attach the C wire but i would do it anyway even if you have decent voltage.
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