I have a Trane X80 furnace with a Nest gen 3 thermostat. This combo has worked flawlessly for a summer and a winter. I just switched back to "cool" and the fan and compressor come on, but the fan stops after a few minutes (while the compressor continues to run). I contacted Nest and after a lengthy list of diagnostics, they determined that the Nest baseplate was bad and sent me a new one. I replaced it and the problem did not change. I pinged Nest again and they said that it must, then, be an HVAC problem. If I jump the fan wire (G) and power wire (R) wire, the fan runs for a couple minutes then shuts down. I'm guessing I have a fan going bad but just wanted to confirm before I replace it.
I welcome and thank you for your input.