Today I was trying to put in my smart thermostat and have had no luck. My old thermostat (pictured below) did not have a C wire connected but did have the wire behind the old thermostat.
After the power not coming on to my new Smart thermostat, I checked the furnace to make sure the blue wire was hooked up to the furnace. To my surprise, there were two blue wires that I found. There was a wire "pack" that had all the wires bundled together (including a blue wire) but that blue wire wasn't connected to anything. On the other hand, there was another lone blue wire that was connected to the furnace. It seemed odd to me that the blue wire including in the bundled wires wasn't connected, and a random other blue one was. Any thoughts on this? Any help is appreciated!
Best Answer
The blue wire at the furnace is likely feeding an airconditioner relay or something that was added later to the furnace. The unconnected blue wire in the "bundle" needs to go to the c terminal so both of them are connected there.