A:Answer A C wire delivers constant 24 volt power to run a smart thermostat. For a typical furnace plus AC system there will be 4 wires and the C wire will be a 5th wire. If you don't already have a C wire, it will likely require making a connection at the furnace. You may have an unconnected 5th wire tucked in the wall. If you feel like you can manage connecting or adding a C wire, there are lots of sites on the internet that have information on doing it. But if you don't feel comfortable messing around inside your furnace, call a technician. It is less expensive to call them before you mess up your furnace.
