Aluminum is a reactive metal protected by oxide.
However when corrosion occous it can literaly
lay the copper coil bare.
You should have the coil coated with a polymer
This can be brought in spray cans and goes
under various names Kole Kote Etc.

"Puddin' Man" wrote in message
...

LIttle 2-ton Heil R22 system, 1 1/2 years old. Cools tiny brick
bungalow in midwest US.

Dogs are all female: no peeing on unit. I hose it down every
time I run the weed-whacker.

Condensing unit fins near ground level turning grey/white with
some kind of corrosion. Doesn't look nice, couldn't improve
heat dissipation.

Spray the corrosion with some kind of preserving lubricant?

Thx,
Puddin'

"Mit der Dummheit kaempfen Goetter selbst vergebens!"
-Friedrich Schiller