While I’m away from home, I like to check in on what’s happening at home using the Sense app. One such time last year, I was having a beer in Mexico City while my house was sitting empty back in the US. Expecting to see few devices running back at home, I was surprised to see a large amount of power being used, to the tune of 5kW. The pattern of power usage showed a large device turning on and off. This seemed very strange, so I looked at the usage pattern closer. A large device would turn on, increase in power usage linearly for a minute or two, then turn back off, only to repeat again a few minutes later. I concluded that this must be the heat pump based on the size of the power use and the ramping-up behavior, and that a safety cutoff must be activating to turn the unit off every now and then. A call to my next-door neighbor confirmed my theory, and he temporarily solved the problem by pulling the cutout.

Ultimately, my Nest thermostat was the cause of this problem, as it had commanded the heat pump compressor to turn on constantly, without turning on the indoor blower. This caused an overpressure condition that cycled the compressor on and off as the high pressure switch activated and deactivated. I was glad to catch it in time that my compressor didn’t burn out!