I live in Florida and my A/C unit is about 15 years old. It still works fine but the outside condenser unit has become a real eyesore. The grille over it is covered with rust. It originally had a plastic coating around/over all of the wires that apparently didn't last in the Florida sun. The plastic coating dried, cracked and peeled away leaving exposed metal underneath to rust. Can I remove the wire grille, brush it down with a wire brush to remove the remaining plastic coating bits and paint it with Rustoleum Cold Galvanizing Compound Spray? Is there a better solution? Even though this old girl looks as rusty as can be, all of the rust is on the grille. Thanks!
For the top grill just cut power, open the access panel, cover the fan so that no paint will get down inside, cover the overside grill and coil and just spray paint the grill. As for the coil grill/guard you will have to take the top off the unit, remove the guard in order to spray paint it.
I would leave it alone. Once you start loosening those grills etc 95% chance it will rattle and be noisy when you put it back together. The screws are rusty and may break. The fan motor and wiring would have to be removed to do the top grill. You may regret it later when it is noisy.