How do you isolate an outlet containing an air conditioner so that the AC won't black out the building?

Isolation is not your issue here!

If the overcurrent protection (breakers, fuses) are sized correctly, and the buildings wiring is sound, the A/C would not normally cause any other problem other than to trip its own breaker or fuse.

If an A/C unit is causing the buildings main breaker to trip, you need to have the electrical system for the building diagnosed and repaired.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS. If you do this work yourself, always turn off the power at the breaker box/fuse panel BEFORE you attempt to do any work AND always use a meter or voltage indicator

to insure the circuit is, in fact, de-energized.