What is causing my AC to trip the breaker after running for about an hour?
If the a/c runs for the better part of an hour, it is almost certainly not a short circuit.

More likely, the air conditioner is slightly overloading the circuit.  Or possibly the circuit breaker has "derated itself."  Fix the latter by replacing the circuit breaker.

Always choose a replacement circuit breaker based on the wire capacity, not the devices connected.  For example, replacing an appropriately sized 20 amp breaker with a 30 amp could easily start a fire from inside the walls.

Addendum:  see the time-to-trip for a line of GE circuit breakers here.  Note that it is normal for slightly overloaded breakers to take hours to trip.