I’m trying to install an ecobee thermostat. My furnace wiring has a red wire at the C terminal, and white wire at the Y terminal which I assume run to the condenser unit because they are bundled together. Then there is the bundle leading to the thermostat. At the furnace the wires are: green on G, yellow on Y, white on W. The red wire on R is very thick and is capped with the skinny red wire leading to the thermostat bundle. There is a blue unused wire also in the thermostat bundle. Can I safely connect the blue wire to the C terminal to use for the thermostat common wire even though it already has the red wire leading to the condenser unit in the terminal?