Progammable Thermostat Common Wire
 

I am installing a new programmable thermostat (Hunter 44860) but would like to have it use the household electricity and not just run off of the batteries. My current thermostat is a 3 wire setup (Y-RC-W, with jumper from RC to RH). I plan on running another wire to connect the common leg to C on the thermostat, but where does it connect to? Currently the RC wire is connected to a 24V transformer off in the basement. Thanks in advance for any help.

On your furnace transformer there is a hot (R) and common (C). Put your new C on the opposite terminal to the RC on the transformer or the C on the circuit board. The return from the AC also has to go to C so you can trace it back from there.