I've been experiencing occasional short cycling of my A/C compressor (turns on/off quickly several times in a row) and Nest senior support is speculating that my common wire may not be properly grounded. Again this only happens intermittently and seemingly random. My HVAC checked coolant levels, coils, etc. All are fine (A/C unit is 6 months old). I've also tried another thermostat (Emerson Sensi) and still has same issue.

Here are pics from the Goodman furnace control board. I do not see any wires screwed into the chassis. Not sure if I'm looking in the right place.



  • Have you tried putting a meter on it? It should show a constant 24V. – john elemans Aug 12 '18 at 16:21
  • 2
    In a building, "Ground" means the Equipment Safety Ground system used by mains power for safety, all the chassis grounding, and bare copper or green wires that run around with the 120V/230V conductors. The C wire, R wire and all that jazz are part of the furnace's low-voltage wiring system. It's a separately derived system and should not be tied to mains grounding unless the furnace manual specifically tells you to do that. Nest doesn't use or need a ground; it's low voltage. – Harper - Reinstate Monica Aug 12 '18 at 16:47
  • Thanks @Harper for that explanation. I am not sure why Nest senior support was so emphatic that the common wire was not "grounded" in such case. I am going to have a technician look for any other possible shorts, loose wire nuts etc that might be causing this intermittent off/on switching of the compressor. – Andy Aug 12 '18 at 19:51
  • @johnelemans I have not but the Nest does provide power readings and they are consistently above 32 volts. I'm going to assume if that is indeed the case that the common wire is properly grounded. – Andy Aug 12 '18 at 19:52

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