Pretty common problem here but the posts I've seen are a little different. New Wi-Fi tstat, no C terminal at furnace but plenty of available wiring at both ends. Unlike others problems posted of unwiring and rewiring, couldn't I just take an available wire and combine it to my G connection at the terminal and then connect wire at tstat? If G controls the fan and I know there is power because I can turn on fan manually, is this the easiest fix?
Thanks
No, because the G terminal gets power from the R. When you turn on the fan on ther thermostat, the thermostat is really just connecting the R to the G terminal.
Internally on the furnace control board, the other side of the relay that actually powers the fan is connected to C. R and C come from the two sides of a 24V AC transformer.
There's almost always a way to get C from any control board, it's just a matter of identifying a C wire from a schematic, or by finding the transformer and identifying how it's wired in.
