I installed a newer version of my existing Nest Stat about a week ago. I haven't had any known issues but I do work too much to really tell. However, today my breaker was tripped to the unit. After a little diagnosis, it seems the Condenser Fan is shutting off immediately as the reversing valve is "flushing". Then the Compressor keeps running... If I turn off the unit via. the Nest app and restart, the Condenser Fan comes back on. My first assumption would be relay, but that's built onto the board (Rheem Heatpump) and turns off as the reversing valve shuts down (thus stopping the fan but leaving the compressor contactor drawn in). Also, the main contactor is drawn in but not stuck, I can pull 24v to it and it will drop out. I'm wondering if there is a way the stat could create this condition... Any help is appreciated!

  • Is in the system in heating or cooling mode? – wallyk Dec 19 '16 at 0:40
  • What model is this system, and is the control board throwing any codes? – ThreePhaseEel Dec 19 '16 at 1:50

It is normal for the condensing fan to stop when the reversing valve changes states going into a defrost cycle from heating mode. This is likely not the cause of the tripped breaker. If the unit is stopped during a defrost cycle and restarted later from the Nest app as indicated, then the defrost cycle in progress will be cancelled. During heating mode, the defrost cycle is controlled by the defrost control board within the condenser and it is not controlled by the thermostat.

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  • I had just the opposite problem years ago. The condenser fan kept running during the defrost cycle, with the result that the outside unit's coil would not defrost because of the cold air being drawn through them. This was during a 20" blizzard. I was out there with a brush trying to keep the coils cleared. Problem turned out to be welded contacts in the fan relay which prevented the fan from turning off. – SteveSh Dec 22 '19 at 2:29

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