I had a really weird issue yesterday where my upstairs A/C unit quit cooling.
Now I've seen this kind of thing before. Usually it means the unit has frozen up. So I checked the line coming out of the upstairs fan unit. No ice. Then I went outside and checked the line around the compressor. No ice. Seemed perfectly fine. The two units' fans are next to each other, and the working unit was blowing out a lot of hot air, while the upstairs unit's fan was blowing out a lot of air-temperature air (kind of refreshing).
So I figure its still most likely ice frozen somewhere I can't get at (or at least I don't know what else to do), so I put in a fresh filter and turn the unit off for 3 hours. When I turned it back on, its been working fine since.
My wife joked about "rebooting" it, but that got me thinking... We actually had two brownouts yesterday. I was here for the second one, and it was so subtle I wouldn't have known it happened except my computer rebooted.
I just checked with my son (who is up there all day), and he told me the same thing happened the day before. We had a very similar brownout that day at 3PM. He checked the airflow at the vent, and the volume was fine (unlike when it freezes), just the air wasn't cool.
So I'm wondering if a really short power dip like this might actually cause a compressor to need to "reboot". I always thought they were entirely mechanical parts, so that doesn't make sense, but I don't know what kind of electronics are in a modern compressor.