Professionals diagnose AC problems through a systematic process. They start by listening to the homeowner's description of the issue and any unusual noises. Next, they perform a visual inspection of the AC unit and related components. Using specialized tools, they check refrigerant levels, electrical connections, and airflow. They may conduct performance tests, such as measuring temperature differentials and pressure readings. This information helps them identify the root cause of the problem. Experienced HVAC technicians rely on their knowledge and expertise to diagnose AC issues accurately and recommend appropriate repairs to restore the system's functionality.