Pin hole leak leads to evaporative coil failure. Majorly noticed on the outside of the coils of unit, due to which refrigerant gas escapes reducing cooling capabilities. Many HVAC manufacturers, Air conditioner manufacturer does not realize various type of corrosion occur in copper coils. The corrosion can be seen like black corrosion, green corrosion or rusting of the coils.
The Failure of evaporator coil can be seen in following