Power Outage - A/C condenser dropped out


One of the big transformers serving the township blew last night; our lights flickered and then I heard my A/C condenser (outside unit) making strange noise. I pulled up the Sense app and something didn’t look right (A/C wasn’t being detected as being on anymore while the power being used was pretty high ~10KW). I shut the unit off for a few minutes, tried powering it back on – no dice (the compressor wouldn’t run). Thought I would be shopping for a new unit tomorrow, but decided to toggle the breakers and the A/C unit kicked back on. Not sure if I would have ended up doing any damage if I didn’t shut the unit off quickly … but thanks to Sense for alerting me.



If you don’t have one, you should consider getting a whole house surge protector, or a surge protector for your outside AC compressor.


I actually do have a whole house surge protector … not sure why it didn’t do anything.


Sometimes there’s a couple minutes or several minutes before the condenser is allowed to be turned back on. It depends from make/model controller. Even thermostats, like Nest, has 2-3 minutes of time allotted before it’ll kick on the AC once it’s turned off at the thermostat or breaker. …but from your story, even I’d be nervous. :slight_smile:


Yeah, most A/C units and thermostats won’t restart the compressor for some minimum time, I think for reliability purposes. Your surge protector didn’t do anything because you didn’t experience a surge (overvoltage), you had a brownout (undervoltage). The brief drop probably temporarily messed up the A/C condenser, but I doubt it did permanent damage. Power cycling it fixed the issue, and waiting the minimum shutoff time allowed it to cool again.

When the capacitor died on my air conditioner last year, it was sucking down probably at least a kilowatt while doing no cooling at all and making unusual sounds. It’s possible yours temporarily got in a similar state from the brownout. (I fixed it myself with a new capacitor from Amazon and a healthy dose of fear from knowing what giant capacitors and big voltages can do to you if you’re not careful.)