if it does not shut off perodically the thermostat control is not functioning properly or the thermostat is set too low and it can not reach the desired temperature.
If the air conditioner will not stop working then the compresser of it should be changed and if not the ideal air control valve should be adjusted. follow the instructions
If your air conditioner will not stop working, I would check to see if you have a problem with your thermostat. It could be reading an incorrect temeperature that would then make the air conditioner to not stop working.