The answer to 'when to replace evaporator coil' is that the evaporator coil in your HVAC system typically needs to be replaced every 10-15 years, or sooner if it becomes damaged or corroded. The evaporator coil is a critical component that absorbs heat from the air inside your home and transfers it to the refrigerant, so it's important to keep it in good working condition.
Over time, the evaporator coil can become clogged with dust, debris, and even mold, reducing its efficiency and causing your HVAC system to work harder. Additionally, the coil can develop leaks or become damaged, which can lead to refrigerant loss and further reduce the system's performance. If you notice any issues with your evaporator coil, such as poor cooling, increased energy bills, or strange noises, it's best to have a professional HVAC technician inspect it and recommend whether replacement is necessary.