Last night I turned my AC down a couple degrees before going to bed. The AC was running at the time, so when I set the temp below the current temp, the blower turned off. After getting in bed, however, I could still hear the hum of the AC unit outside. I went outside to be sure. From the thermostat I turned the blower to manual, and sure enough, cold air came from the vent. I turned the blower off, the AC continued to run...

I then turned the thermostat from 'cool' to off. Still, the AC kept running. I wan't really sure what to do because it was 11pm. I unplugged and plugged back in the thermostat. Still it continued running...

Eventually, maybe 20-30 minutes after initially adjusting the temp, the unit finally shut down. I turned the thermostat back to cool, now set to 78 degrees, well above the current temp. The next morning I turned the temp down, the systems came on as usual, and after a few minutes, shut down as usual -- twice before I left for work.

Is this a one-off thing? Should I have the system serviced?

Also, the AC is on the interruptable circuit, but the light was green (circuit open) when this was all happening.

Any ideas? Thanks.

  • 1
    When you say you "turned down the AC", do you mean you set the temperature to a colder or warmer temperature?
    – wallyk
    Commented Jul 25, 2016 at 16:52
  • 1
    Is it a cooling-only unit, or is it a heat pump? Has the system worked okay before? Is it recently installed/upgraded?
    – wallyk
    Commented Jul 25, 2016 at 16:53
  • Usually AC units cannot be cycled on and off quickly. They take time to reset once they are off until you can turn them back on again.
    – ArchonOSX
    Commented Jul 25, 2016 at 17:54
  • The system is around 14-years-old, and is a cooling-only system. I also have a gas furnace -- necessary here in MI. By, "Turned the AC down," I mean increase the target temperature on the thermostat.
    – BenW
    Commented Jul 25, 2016 at 19:59

1 Answer 1


It was a sticky relay. I should have just hit the AC unit and the relay probably would have un-stuck, but only to have gotten stuck again later. I could have just cleaned the relay too, but I had the HVAC guy replace it with a new one he had on the truck.

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