Method Development for Evaluating Microbiological Growth on and Attachment to Aluminum Air Conditioner Evaporator Core Surfaces

Corrosion failures of aluminum air conditioner evaporator cores have been reported in regions where the climate is relatively warm and humid. Microbiologically-influenced corrosion [MIC] has been implicated in these failures. Application of surface-treatment chemicals may inhibit microbiological (bacterial) growth and/or attachment, thereby reducing the potential for MIC.

In this study, two laboratory methods were developed to evaluate selected surface-treatment chemicals for their ability to inhibit bacterial growth and reduce bacterial attachment to treated surfaces. Using the developed methods, two controlled-atmosphere brazed aluminum core materials and three surface-treatment chemicals were evaluated. Neither of the untreated core materials was found to inhibit the growth of the bacteria tested. Among the surface treatments, Product A did not appear to be inhibitory towards either of the bacterial species, however attachment of bacteria to the treated aluminum coupon was reduced by 32-39% after one hour of contact and by 57-67% after 48 hours of incubation. Product B appeared to be inhibitory towards both of the bacterial species tested, but did not seem to affect bacterial attachment. Product C also appeared inhibitory towards both species tested and reduced attachment by 60-80% after 48 hours of bacterial contact. These results were generally consistent with manufacturers' claims about the functionality of their products.