Nest Thermostat Causing Short Cycling

Smart thermostats require constant power for their touch screen, WIFI, etc. A smart thermostat usually gets this power via the common wire, or c-wire. Before smart thermostats there was no need for constant power at the thermostat, so older systems typically don't have the c-wire.

Nest thermostats work off an internal battery. In the absence of a c-wire, the Nest thermostat charges it's battery by running the HVAC system - short cycling.

Here is a link to a professional HVAC tech forum thread with some techs around the country answering a homeowner’s question as to why they think, or their personal experience with clients, as to why Nest thermostats are potentially harmful to HVAC systems LINK. This is just one thread of many on this professional site on this subject.

It would seem wise on your part to replace the thermostat with a Honeywell or Ecobee thermostat with similar capabilities that are known not to potentially cause such issues.

Old Thread

Same thing happened to me! I had a friend connect the common wire I found in the wall to the unit in my attic and I haven’t had an issue since.

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It would seem wise on your part to replace the thermostat with a Honeywell or Ecobee thermostat with similar capabilities that are known not to potentially cause such issues.

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Have 2 Honeywell Smart thermostats, with one of them nearly 8 years old. Works great and has built-in protections to not short cycle the compressor and has a 5 minute delay for brownout protection if there's an outage.

But another way to protect against short cycling would be a solid-state contactor like this one. It has brownout protection to prevent the compressor from short cycles.

LINK