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Here's a request: connect the fucking c wire! It's 2021. If folks don't have a smart thermostat, it's pretty likely they will before the furnace needs replaced and it doesn't take a genius to install them either. If you can take the time to wrap the wire around the cord, you just as easily can connect it if available.
Quick summary: I got a new furnace in 2019. They did not connect the c wire to the current wiring setup, even though I had a cheapo smart thermostat with the c wire connected to it. It wasn't an issue because it had alkaline battery backup. Now I upgraded to nest and according to Dr. Google, while not required, the c wire is pretty important to prevent battery drain on the nest. Without the c wire, it only charges when the air handler is on pumping heat/cool air. So if I keep my windows open for a week with everything off, my thermostat could run out of juice and not turn on when I want it to...requiring me to charge it.
The blue wire is what I need to connect. Should likely be an easy fix but this turned a 15min thermostat installation into an hours long ordeal of troubleshooting. So annoyed.