C wire spliced and connected to the Y terminal?

Behind my old thermostat I have only 4 wires. Red, Green, White, and a Blue wire connected to Y. I figured I just need to go to the furnace and connect the C-wire extender to the board.

When I got down there I found this and am confused on what to do next. The spliced wire and the blue wire are connected to the Y terminal (you can’t see it in the pic) The board is set at G, COM, W, Y, and R in case this isn’t clear.

Looks like I do have a C-wire but it’s not run up through the wall. Does anyone know what my next step should be?

the white & red wires in the other cable are going to the outside condensor, these wires need to stay on the board. you’ll need to install the C wire adapter. just follow the instructions in the app, you will add the C wire from the adapter to com 24v terminal, along with the existing white wire that’s already on it.


So I should put the c-wire adapter wire on the C terminal with the second wire? And do the same with the spliced wire on the Y terminal along with the c-wire adapter wire?

Yes, you’ll have 2 wires each on C & Y


Thank you very much, Ken! I appreciate your help.