Your AC compressor is controlled and it's not always on when you turn it on so it can do its cycling thing.
That fucking compressor is expensive. What's happening is your relay is getting stuck in the on position and activating the clutch. That is a common issue. Eventually you'll leave your car sitting and it'll bring the battery down to zero. That can happen if the relay continues to malfunction when the car shuts down. If the compressor doesn't get relief once in a while the pressure will release the refrigerant one way or another.