The traditional HVAC system consists of a furnace, a fan, and an AC system, and you need four wires for the system to work.
For modern HVAC systems that use a smart thermostat, you need to connect a C wire.
Thus, you will need to have five wires for your HVAC system and the thermostat to function. To access the wiring, turn off your HVAC system to get to the control board to show which wires should go where you fix them. Then open the HVAC units’ covering and access the control board. The control board will have terminals labeled R, G, Y, W, and C, with each of these terminals corresponding to wires routed to your thermostat. The typical color codes for the wires connected from the furnace to the Thermostat are Yellow for cooling, Green for the fan, White wire for the heat, and Red for power. There are instances where a blue wire will be used for cooling, depending on the thermostat’s brand. The blue wire will be the common wire for a five-wire thermostat, also called a C wire. If you attempt to install on your own without professional help, take note or take a photo of every wire and where they are connected in the HVAC controlling board and match them on the thermostat’s terminal. When you incorrectly wire them, you may end up blowing a fuse, or your system may not function properly. You should wire your HVAC system correctly to ensure it runs efficiently. Better yet, get an HVAC professional to wire your thermostat.