How do I know if my air conditioning compressor over heats?

All condensing units have thermal overloads built into the motor windings. Some units have external potential relays and current relays. If the unit motor overheats the overloads or relays will open and the motor will stop. The fan motor will continue to run. The unit is cooled by the refrigerant and the condenser fan motor. High refrigerant charge can slug a compressor and cause high heat. Keep the outside and inside coils clean, change filter regularly, don't open doors too much during high humidity/high outside heat conditions and you should be ok. If a motor shuts off because of thermal overload it will come back on in 20-45 minutes automatically. If anything happens to your inside blower fan motor the outside unit will overheat within minutes.