Ecobee Common Wire Question

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BetsyJean

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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?

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Jadnashua

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Assuming you have an air conditioner, it needs the common so when the thermostat calls for cooling, it has a complete circuit (often, the yellow wire). Yes, you should be able to attach the blue wire to that common terminal and use it to power the thermostat.
 

BetsyJean

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Assuming you have an air conditioner, it needs the common so when the thermostat calls for cooling, it has a complete circuit (often, the yellow wire). Yes, you should be able to attach the blue wire to that common terminal and use it to power the thermostat.
Thanks so much for the reply. I read another forum with someone in the same situation as me but their red and white wires to the ac condenser were reversed on the furnace terminals. Their red wire was on the Y terminal and white wire on the C terminal. I know wire colors aren’t always standard but wanted to make sure this wouldn’t cause any issues utilizing the C terminal for the thermostat power in conjunction with that red wire from the ac unit.
 

Rod Kahn

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I heard that the red/white cable to the outside condenser doesnt matter which way. AC current. but by convention red is hot, white is common.
 
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