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Coil Corrosion


Formicary Corrosion | Rev Corrision | Tell Us About Your Coil Leak

Formicary Corrosion

Recently we have encountered an unusually high number of indoor cooling coils developing leaks, typically between one and three years from installation. We have actually replaced more leaking coils in 2011 than the entire time Bailey’s Heating & Air, Inc. has been in business-over three decades. We were so concerned by this alarming trend that we invited a factory representative from Lennox (the main brand we were selling at the time, and subsequently the source of nearly all our leaking coils) to come visit seven homes with identified leaks. After the visit, Lennox sent us literature claiming that the leaks are caused by formicary corrosion.

  Formicary corrosion, also called “ant nest corrosion” due to its resemblance to ant burrows (see Figure 1 for a cross-section of corroded copper), is a form of metallic corrosion resulting from the chemical reaction between a mixed-metal coil’s copper tubing, aluminum fins, moisture, and off-gassed volatile organic compounds from inside your home (such as cleaning products and other chemicals).
Fig. 1 (Formicary Corrosion)

Our own experience with coil leaks (or rather, the hitherto lack thereof) motivated us to do some research of our own. Figure 2 shows the location of five leaks discovered in a three-year old coil after pressurizing it to 300 PSI test pressure and placing it in a dunk tank. Figure 3 is a picture of the corrosion found when we cut out a section of this coil, removed the fins, and examined the copper tubing under a microscope; as you can see, there is extensive and deep corrosion all over the copper. For comparison, we did the same to a twenty three-year old coil, figure 4, that had no previously identified leaks, and found a normal amount of corrosion for its age, but still nothing comparable to that found in the newer, three-year old coil.

Fig. 2 (Coil With 5 Leaks) Fig. 3 (Corrosion Magnified 40X)
3 year old R410a Coil
Fig. 4 (Corrosion Magnified 40X)
23 year old R22 Coil

Our findings so far have been consistent with our experiences from the 35 years we have been in business, installing tens of thousands of systems. Despite what Lennox claims, the air inside your home has changed little over those 35 years, yet only recently have leak issues arisen. The sole common denominator amongst our leaking coils is R-410A refrigerant. Beginning in 2010, legislation phasing out manufacturing of equipment using R-22 went into effect, and even as early as four years ago, manufacturers were choosing to make higher-efficiency equipment for use with R-410A refrigerant rather than R-22.

Manufacturers maintain that R-410A cannot be the cause of these leaks because the corrosion is forming on the outside of the tubing rather than the inside, where the refrigerant runs. However, given that the only variable which has changed over time is the use of R-410A, we suspect that differences between it and R-22 (its use of synthetic oil and higher pressure, for example) correlates directly with the corrosion causing the coil leaks. Given that there is no replacement for R-410A refrigerant, leaks caused by such would be a costly problem for many manufacturers- it’s no wonder that they are turning a blind eye toward what we hypothesize is the real cause.

Let’s look at this from you, the customer’s, point of view. If it is truly the chemicals in the air inside your home causing the formicary corrosion, then replacing coils solves nothing, as we have not changed the air in your home. Won’t the leaks reoccur? What happens when your warranty expires? Will you have to come up with thousands of dollars to replace these coils when they are out of warranty?

We here at Bailey’s are not standing idly by hoping something will happen to resolve this issue. As discussed above, we have begun new procedures and tests to help quickly identify leaking coils. Now, when we service a piece of equipment, regardless of whether it is R-22 or R-410A, Lennox or another brand, we are taking water samples from the condensation off of each coil and testing them to record their pH levels. By the end of next summer, thanks to these pH analyses and other data we are compiling, we will have a more complete understanding of this problem and possibly some solutions, or at least more proof of what is really causing the leaks. We have also constructed our own in-house testing facility to diagnose failed products, identify the issue, test solutions, and keep ourselves on the forefront of technology when it comes to our customers, the products they have purchased, and their comfort.

One of the most important changes we have made as a result of our research and investigation is switching which brands we sell. We are now Trane Comfort Specialists- in fact, we are the only Trane dealer in the Modesto, Turlock, Tracy and Stockton area. We became a TCS dealer because we now feel Trane has the best equipment on the market, particularly due to the fact that they are one of the only two manufactures who manufacture the majority of their coils from solely aluminum (thus avoiding the corrosion problem found in copper-aluminum coils). Trane had the foresight to realize the problem posed by mixed-metal coils and smartly avoided it by changing their coil manufacturing to aluminum.

To sum up, I personally believe that manufacturers are being incredibly short-sighted. The manufacturers are blaming formicary corrosion on only one component of a complex process, and even if they were correct, they offer no recourse to prevent the corrosion in the first place, nor an explanation as to why this corrosion is so prevalent and extensive only in systems installed in the past few years. We here at Bailey’s believe you deserve better, and we are taking steps to make sure that the products we install provides trouble free service for the years to come. In closing, I would like to say that we appreciate all our customers putting their trust in our company over the years. We continue to work our hardest to ensure that you are receiving the best equipment and information that is available.

Mitch Bailey