Nest Learning--On, Off, then On again in rapid succession

[mdmcalor]

Have 2 Nest learning thermostats that are about 2 years old.  Approximately 2 months ago they started to cycle oddly. They turn on the units for maybe 2-3 second, shut off for maybe 3-4 seconds then restart.  Does not happen every time they switch on however, the instances are becoming more frequent.  A/Cs are 2 and 6 years old and are seviced regularly.  Had the tech out for this specific issue yet he was unable to figure out why it happens.  Hoping for an answer as I am worried this will damage my units.  Thank you for reading.

[CoolingWizard]

@mdmcalor The potential for damage is very very small. The compressor is not running long enough to create a refrigerant pressure difference.  If your outdoor unit has a control board it will protect the compressor from short cycling and power outages.  

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AC Cooling Wizard

[mdmcalor]

Thank you for the info. It does alleviate some of my concern.  However, since it happens to both systems, could it be an issue with the Nest wiring?

[CoolingWizard]

@mdmcalor I am not sure of the root cause the symptoms you are experiencing.  If the system works fine after the 2-3 second On-Off-On episode, there cannot be a wiring issue. This is most likely caused by the thermostat or the furnace/air handler control board. 

AC Cooling Wizard

[brianpgay]

I just replaced my thermostat with a Nest and it rapidly turns on and off over and over every 2 seconds or so, again and again continuously. Must be a wiring problem. I think there was  blue wire that the old thermostat did not use, so I did not use it with the new Nest.

[CoolingWizard · Accepted solution]

@brianpgay ,

if the entire system is turning on-off-on, it can damage the compressor.  Most systems have a safety interlock that puts a 5-minute delay on a restart.  

Check the power level of the Nest battery.  If possible use the blue wire and supply a power common for the Nest Thermostat. 

AC Cooling Wizard