Here's a pretty good article that describes the problem:

Here is a link that might be useful: Troubling Pinhole Leaks in Evaporator Coils Cause Corrosion Issues

That copper pipes are black might be a clue....

Replaced any drywall recently? Around here, there is a major court case concerning Chinese made drywall that out gasses sulfur compounds. Wiring and piping in affected homes rapidly degrades in these recently-built homes to the point that *everything* has to be ripped out and replaced

The courts have ruled in favor of the homeowners in at least one class action lawsuit, but actually collecting from the Chinese is another matter.... Hope you don't have that drywall.

This post was edited by apg4 on Mon, Jul 14, 14 at 15:22

It is difficult for me to believe that the use of cleaning and personal hygiene product chemicals in the home is going to cause a corrosion problem. I'd love to see some data that could support that. What I am thinking of is exposing a coil to, say, 10 X the high side of what you find in a typical home and show what happens.

Formic and other organic acids in building materials, in drywall and other things, is a known problem. The OP should look at his pipes and wires.

This post was edited by ionized on Mon, Jul 14, 14 at 21:20

It is not Chinese dry wall. We thought of that last year also, but I have not had any constuction done on the home. I'm sending my AC rep the Article that was shared. Thank you. He replaced my coil today with an all-aluminum coil since something is clearly attacking the copper. I will let him know about the 3rd post; the notation on testing on a 10. I am sure he will know what that means because I am the home owner and do not. Thank you for replying and giving us something else to look for!

I fixed my post. It should be 10 X as in ten times.