I went to the Armor Coil web site and found something that you can buy at Home Depot called Rustoleum ....for less cost. There are some issues.
Yes a thick paint can form a wall against cloride based corrosion but does the spray penetrate all the way to the fin coil joint where the corrosion impacts the unit the most? Does the paint reduce the fin gap and force the fan to run longer to move as much air for heat transfer? Does the paint block heat transfer? Does the paint peel off at the edge? Does the paint have a soft surface and get dirty easily? I suggest that there are other options that have been proven by third party testing, endorsed by OEMs and demonstrate energy savings as well as corrosion protection. Try www.adsil.com