I'm having an issue with my NEST thermostat short cycling my air handler fan while in running AC. This is a known issue, and the fix seems to be adding a common wire to the NEST.
My thermostat is wired with 18-5, and currently the yellow wire is unused. I want to use this for the common. Pic of the board is attached. Humidifier and AC compressor are wired to board.
Can I just add the Yellow wire to the C terminal without changing anything else? I should probably pigtail the 3rd wire, correct?
Sorry for the dumb questions, I just want to make sure I've got it right.
ETA: Picture of terminal block
Left to right: R C W Y G