Why is the breaker tripping

If you unplug the air conditioner and turn the breaker on does it still trip? If so you have a wiring issue within the circuit. If not then the issue is with in the air conditioner or the circuit is getting overloaded. Make sure the air conditioner is off when you plug it in or turn the breaker back on. If it is not an issue with the circiut then there has to be something shorted inside the unit. A wire could be touching the cabinet inside.