Cross reference the wiring of the existing base layout with the nest base wiring diagram. The thermostat base is compatible with a TON of systems and wiring configurations. It can even utilize custom configuration.
Just checking in to make sure that you've seen our responses. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.