Thanks for posting to the Google Nest Community forum! I'd be happy to take a look into this for you.
Some HVAC systems, called dual transformer systems, use separate power sources for heating and cooling (Rc and Rh). If you have both an Rh and an Rc wire, you have a dual transformer system. Only the Nest Learning Thermostat 3rd generation will be compatible with your equipment.
Feel free to let us know if you have more questions in mind.
I just wanted to follow up to see if you still need our help. Please let us know as we would be happy to answer any questions you may have.
I appreciate the help, Mark.
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.