To diagnose a noisy condenser fan, start by inspecting the fan blades and guard for signs of damage or wear. Check for loose screws, bent blades, or debris accumulation. Next, inspect the fan motor for signs of overheating, worn bearings, or electrical faults. Use a multimeter to measure the motor’s voltage and current draw. Compare the readings to the manufacturer’s specifications to identify any anomalies. Finally, perform a visual inspection of the condenser coils to ensure they are clean and free of debris.