Two issues I've encountered:
So, any ideas for how to proceed here? Thanks!
The sub-base on my Nest 3rd Gen Learning Thermostat has failed. I called an HVAC technician to diagnose the problem. He discovered that "Continuity is constantly being passed through RC to Y1 on the sub base."
In other words, there is a bad connection in the thermostat hardware that causes my air conditioner to constantly be running. The only way to shut it off without replacing the hardware is to remove power to the HVAC system.
The warranty-claim form on the Nest web site does not work.