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1

The C wire is one side of the transformer and the R wire is the other. The R wire feeds the signal into the thermostat where relays connect that voltage to G (fan), Y (cool) and W (heat). In the furnace control board, G, Y and W are sinks not sources, so you should get a small voltage reading or zero, depending on your meter from R to any of those three. You ...


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The only thing that could be happening in this case is a broken wire, or a bad splice. A solid, continuous wire will have voltage on the other end, even if its partially damaged. A damaged wire will not have the current carrying capacity (amps) that a good wire does, but it will show voltage. Also, since this is alternating current, the 2 volts you're ...


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For the A/C zones -- Nests need the C wire from the cooling side One downside of the Nest in a two-transformer application is that it requires that the C wire come from the same transformer that is powering the cooling side of the house (Rc, Y, G, O/B). Fortunately, this works for the two Nests you have that are controlling both heating and cooling, so you ...


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The thing to consider is that each thermostat is getting power from somewhere, and where the C-wire comes from needs to match that. For the furnace thermostats, the C-wire needs to come from the same transformer that the red wire comes from. Its possible that multiple units share a single transformer, but that's not likely. I would assume that each unit ...


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