I have a unit that developed a refrigerant leak due to corrosion of the evaporator coil. The unit has been in service for a little over 4 years.
The corrosion seemed to be limited to the copper only and only in areas that were exposed to the condensate water. The corroded copper is green in color and the green corrosion even flakes off in small flakes. An interesting clue is that the aluminum fins were still bright and shiny although now had a patina of green copper corrosion residue. Whatever process was corroding the copper appears to have had NO effect on the aluminum fins.
I found some information on formicary (ants nest) coil corrosion, however, this doesn't seem to match. I am seeing a green residue whereas formicary corrosion leaves a red residue. I also found some reports of corrosion related to "Chinese drywall" however this house is 33 years old so this is not an issue.
Have any of you seen this green copper corrosion before and know the process that causes it? Obviously once I know the cause I would like to know how to prevent it.