My ac unit works sporadically. Today it cooled

First check your filters to make sure they are clean and you have proper airflow.

If they are clean, then you either have low refridgerant or dirty coils.

The outside coils can easily be cleaned by disconnecting power to the unit, then using a water hose to spray off the dirt, grass, etc.

The inside coild can be very difficult to get to on some units and require a special evaporator coil cleaner. As for adding refridgerant, the Law requires one to be certified for purchasing or working with refridgerant so you may need to call a service tech for that. Expect a bill from $100 to $225 for a typical system recharge depending on how low it is and which company you call.