Thanks for reaching out. Some systems, including heating-only, cooling-only, zone-controlled, and heat pump systems, require a C wire or the Nest Power Connector. You can click on this link to learn more about this.
Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.