Your current heat pump system has a secondary stage of cooling/heating. With that said, your Nest Thermostat doesn't have a terminal to accommodate the AUX wire which is intended for the secondary stage of cooling/heating. You can still use that and not plug in the AUX wire, but I suggest replacing it with the Nest Learning Thermostat so you can fully get the most out of your heat pump system.
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.
