I'm working on adding a smart thermostat, and as many older setups have it, my current thermostat doesn't have a 'C' wire.
However, if I pull the wires further out from the wall, the feed from my A/C air handler has 'extra' wires.
I would guess the blue colored wire may be C, but I'm not sure, and I'm not sure it even has power. I would like to check that it has 24+V, but I'm rusty on my electrical diagnostics. With my multi-meter (set on stun, I mean Volts) would I use Red to the blue wire and Black/common to ... some other wire? If so, which one?
Update: I added an image of the wiring at the air handler. I noticed that the white and blue wires are disconnected there. If I knew where I needed to, I could connect the blue wire.
If the white wire was connected, the Ecobee I'm connecting has an adapter that would make it work without the C.