I am looking to install a new thermostat that will require a C wire. I have a single stage A/C unit and my current thermostat has Rc, G, and Y wires. There is also an unused blue wire which I traced to the A/C unit electrical panel - it is not connected to anything. My problem is - the guys that installed my A/C were kind of "half ass" and there is no easy way for me to just connect the unused blue wire in the A/C electrical panel. The unused blue wire is wrapped around the brown wire.
You should be able to see onto the board where the rest of the wires connect and find the "C" terminal. It likely already has something connected going to one of the many wire nuts (and yeah, that is pretty sloppy).
You can test for sure using a multimeter. Set it to measure AC voltage, and then between the Rc (or Rh) and C wire you will see around 24VAC.
Once you've traced C and verified it, connect it up to your blue wire. Do yourself (and anyone who works on this in the future) a huge favour and label each wire at the thermostat before you put it back in the wall.
