electricalhvacthermostatthermostat-c-wire
I've searched multiple threads regarding this, but I didn't manage to find any that seemed to match my use case. My board doesnt have a C terminal, and it doesn't have the other terminals connect to the transformer like a lot of diagrams show. Where can I place the spare wire that I'll be using as C? Thanks in advance.
In the photo that shows the insides of the furnace. On the left side of the photo there's a yellow and a red wire connected together. That should be where you want to connect the C wire.
you can confirm this by tracing the wires. From the thermostat cable, the red wire should connect with the blue and orange wire. While the blue wire connects to a white wire, with a blue twist-on wire connector. There's another blue twist-on wire connector where two red wires connect. One of the red wires is grouped with the white wire (in the same cable), those go to the A/C. The other red wire should run over and connect to the yellow wire, using a yellow twist-on connector.
If all this is true (it's difficult to trace the red wires through the photo), then the yellow wire from the thermostat cable (new C wire) should connect with the red and yellow wires.
Based on your description of the wiring, and the schematic you've provided, this is what I think is going on.
Click for larger view
It sounds like there's a white wire and a black wire, connected to the secondary side of the transformer. The white wire carries 24VAC to the thermostat, which means the black wire is connected to the C terminal.
So the new thermostat should be wired as follows:
RWCYou can verify this by measuring the voltage between the blue and white wires, in the diagram above. You should get ~24 volts AC, though it might be a bit higher or lower.
Best Answer
Attach it to the junction of the fat blue wire and the skinny red wire
Since it appears like you have air conditioning, as the yellow wire from what looks to be your thermostat cable goes off to what looks like a connection to a white wire in a two-wire cable, likely running to the outdoor unit (compressor).
Because of this, we can make a good guess that the red wire from that two-wire cable connects to a C wire, and that guess is supported by the wire color scheme; the wiring diagram calls out the C wires as blue, and sure enough, the wire that red wire connects to is blue indeed. So, I would try incorporating the C wire to your thermostat into that bundle, then.