I had a bizarre problem develop yesterday. One of my AC compressor units started running even though it was only in the 40's outside. Checked the Nest thermostat for that zone and it showed that it was in heat only mode. However, the thermostat was reporting a temperature 10 degrees warmer than it really was in the room. Thinking the problem was with the thermostat I switched it with the Nest from the other zone. Different thermostat, same problem: reporting a temperature 10 degrees warmer than the room and AC compressor running. I ended up just turning off the breaker for the compressor unit, but I am guessing the problem is with a relay leaving the AC stuck on. That doesn't explain why the Nests are reporting temps warmer than it really is, unless the electrical problem somehow is raising the temperature of the unit. Any insghts would be appreciated, since the HVAC tech's first instinct is going to be to replace the Nest which isn't the problem from what I can tell.