Dometic Penguin stuck blower motor
Mine will do this from lack of use, especially when sitting long periods in wet weather.
While I'm not sure all of these air conditioners are prone to this condition, I have learned to exercise mine monthly to keep the motor free.
The solution, if stuck, is relatively easy. Try a couple quick attempts at "fan only" and don't hold the power on to a stuck motor. If a few very brief attempts fail to free the fan, go on roof, remove shroud, and spin the squirrel cage by hand.
On mine I suspect it is dirt and corrosion locking up the squirrel cage blower or the motor's armature. Once free and spun around a few times by hand, the bearing is silky smooth.