After 17 years of servicing and repairing AC units in the coastal Florida region, Advanced Air and Heat has witnessed the damage caused by salt air exposure to countless condenser coils. Bare aluminum fins can deteriorate rapidly because of their design, the location of the equipment relative to the salt water, and maintenance. A typical indication of corrosive damage is visible in the disintegration of the fin, often resulting in aluminum flaking. In severe cases, strips of the fins will peel away from the copper tube, disrupting the mechanical bond to the tube and reducing the finned surface area. This damage stops the A/C unit from transferring heat out of the air conditioned space. Some of the disintegrated fin material can be pulled into the coil, obstructing airflow and further reducing overall heat transfer.
Condenser coil degradation impacts the entire mechanical cooling system. As the coil surface deteriorates, the coils can no longer transfer heat according to design specifications, thereby decreasing efficiency.
Head pressure begins to increase, causing shutdowns from the high-pressure limit system. Compressors and condenser fans must work harder, drawing more current and shortening their life. This results in increased energy costs and premature component failure. Consequently, the equipment owner will face higher operating and repair costs.
Find The Right Solution
Many products are designed to preserve the fin surface of coils located in corrosive environments. Alternatives to combat fin deterioration include using copper instead of aluminum for the fin stock, coating the aluminum fins with an anti-corrosion material, and in-place wash systems.
Copper fins are double the cost of aluminum fins and suffer the same downfall, just at a slower rate. Coating manufacturers suggest a variety of compounds and application techniques to protect fins from corrosion, like baked phenolic coatings. However, baked phenolic coating is brittle and tends to chip or detach from the fin surface due to thermal expansion and contraction caused by temperature fluctuations.
One challenge in the application of spray-on coatings is getting total coverage of the finned surface. Any coating is only as good as the preparation of the surface to be coated. If the coating oils and other surface contaminants are not removed, it will not adhere properly.
We have tested many methods to protect coils from salt air corrosion. So far, the most effective protection is to use standard materials of construction, copper tubes with aluminum fins, and a galvanized case coated with a polymeric dipped coating. The polymeric coating has elastomeric qualities that flex with thermal expansion and contraction. The dipping process ensures that the total fin surface, including niches that might not be covered by spraying, is coated.
Again, the coating is only effective if it maintains adhesion to the metal surface. Proper preparation of the bare metal is essential.