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The fins on my external AC seem to be heavily corroded by misplaced canine excretions:

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Two 50 lb male dogs, about 5 years worth of misplacment.

As is, the AC cools the house more than adequately, and we only run the AC a few days per year so we are not worried about the extra load on the system (or should we?).

Since the fins are on three sides, the dog-urine corrosion seems equivalent to not having 1/10th to 1/8th of the cooling capacity of the radiator. Some of the corrosion is 100% in the sense that it seems it would just powder away down to the R22 pipe.

Cleaning away the corrosion will open up big passages from the outside to the inside, thereby reducing the fan driven air flow over the remaining good-condition fins, thereby reducing the cooling capacity of the radiator even further. It'll be worse off than leaving it be.

Is there a way to revamp the corrosion area without opening pipes of this 10+ year unit?

Maybe clean away the corroded fins, then sister on finned 'half-pipes' on either side using an epoxy/adhesive/liquidmetal with good heat transfer properties? Or instead of adhesive, zip-tie the half-pipes in place with a thermal paste in between the half-pipe and the existing R22 pipes?

Or maybe leave the corrosion alone, upgrade the fan to increase the air flow? But we don't want to leave the corrosion in place if it is going eat away the R22 pipes more than it already might have done.

We only use the AC a few days per year, 100 hours per year at most, so short of regaining cooling capacity, it would be worth the effort if I could do something keep the corrosion from eating away at the R22 pipes themselves.

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A non acid foaming coil cleaner is your best option at this point. Once the fins are gone the coils will still exchange some heat but not be very efficient. R22 is getting very expensive ( around $100 per pound) . Since the coils are damaged cleaning all 3 sides will help the system Cool possibly for a few more years. I would not try to add epoxy or other adhesives to the coil. Cleaning with a foaming cleaner and low pressure water (no pressure washers) just a garden hose may stop the corrosion and improve the condenser coil's heat exchange.

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  • Why do you advise against adding finned half-pipes along the corroded areas? What about the big passageway(s) created when the corroded area is 'cleaned' up? The holes are going to severely reduce the air flow over the remaining good fins. Once clean, how can the residual oxidation on the pitted aluminum fins and copper R22 pipe be neutralized so that it doesn't seed further corrosion? Similar to iron rust, is there a rust converter for aluminum and/or copper?
    – Billy
    Aug 7, 2016 at 16:14
  • oaktrust.library.tamu.edu/bitstream/handle/1969.1/4580/…
    – Billy
    Aug 7, 2016 at 16:37

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