Existing system has two C wires

[Iwan22]

My existing system has two C wires hooked up, what do I use for my new nest learning thermostat? Both? Pick one?

Existing system has these wires connected: C, C, Rc, Y, W, G

thanks

[Jenelyn_O]

Hi Iwan22,

Thanks for checking it with us. I'd like to know more about it. A few questions: in what country are you located? What is the make and model of your system? Could you please take a photo of the wires connected to your system's control board? Ensure that the labels of the wires are visible. 

Best,

Jenelyn