AC units are rather demanding as far as electricity goes. As such, they’re liable to trip your breaker while they run. If you’ve noticed that your AC unit doesn’t work, and the breaker has tripped, then you should shut down your AC unit at the thermostat (switch the thermostat to “Off”). Then, you can switch the breaker. Wait 30 minutes as the system resets. Then turn your thermostat back to its previous setting, and make sure that you hear your AC unit turn on.