The answer to 'when to replace evaporator coil' is that the evaporator coil in your HVAC system should typically be replaced every 10-15 years, or sooner if it becomes damaged or significantly degraded. The evaporator coil is a critical component that absorbs heat from the air in your home, and over time it can become corroded, clogged with dirt and debris, or develop leaks that reduce its efficiency.
Replacing the evaporator coil is an important maintenance task to keep your HVAC system running at peak performance and prevent more costly repairs down the line. Signs that it may be time to replace the coil include reduced airflow, increased energy bills, and visible damage or corrosion. If you're unsure, it's best to have a professional HVAC technician inspect the coil and provide a recommendation.