Don’t Paint Air Conditioner Coils

Question:

I just finished reading your answer to B.L. in December’s issue of Products Finishing. I work at an air conditioner coil manufacturer, and we paint many coils. However, this is one application where I do not recommend painting. You are so right about the Faraday cage effect of electrostatic painting of coils. Outdoor condenser coils over one row deep are very difficult to paint and to get complete coverage inside. If you fail to get complete coverage, you are promoting the corrosion at the uncoated areas because of surface area relationships. The small uncoated aluminum area will corrode much faster than if it was not painted at all. To get a good protective coating for this application you need a dip or immersion coating rather than a spray application. Also, paints that provide good corrosion protection usually do not have good UV protection.
The loss in efficiency because of the coating (usually 1-2 mils) is very small (usually less than 1-2% for the coil or approximately 0.3% for the system) compared to the total system inaccuracies (usually 5-10%).

The best solution to this problem is to have an all copper coil and then galvanic corrosion is solved—no corrosion, no loss in performance. J.H.

Answer:

Telling people not to paint their products is heresy, J.H. I was reluctant to write this for fear of losing my membership in the Pittsburgh Society for Coatings Technology. Even as I wrote, I had visions of paint salesmen, armed with spray guns, storming my office. On the other hand, maybe you have the right idea. Use of the unpainted copper-tube/copper-fin condensers will solve two problems. There will be no Faraday Cage effect and no galvanic corrosion. I have no clue about the ease of producing copper fins. However, if it works for you, it could work for others. In any event, it sounds like a good alternative approach to solving a serious corrosion problem. However, if copper-tube/aluminum-fin air conditioner coils must be painted, electrocoating is the method of choice..