It’s a word sure to trip up even the best spellers at the National Spelling Bee, and it’s still causing its own issues in HVACR. The word is ‘formicary.’ If one of those young spellers was to ask for a definition, it probably would be best not to ask contractors or service techs, as their answers may have a few choice expletives thrown in.

But, in fairness to all sides, the industry has been coping with this form of coil corrosion for decades and is making strides in the battle against it.

In the June 11, 2007, issue of The NEWS, Montevido, Minnesota contractor Dave Mitlyng, who has since retired, discussed formicary concerns after encountering an odd pattern of evaporative coil failures. There were pin holes on the outside of the coils, which allowed refrigerant to escape and let air and other non-condensables into the system. He said a colleague told him contractors down South call the problem “ant nest,” adding that the higher pressure of hydrofluorocarbon (HFC)-410A could be making the problem worse.

“The problem of ‘ant nest’ coil corrosion is not really a new one,” Mitlyng said in the 2007 article. “It has little to do with R-410A in the system. Formicary (literally ant nest) coil corrosion has been occurring throughout the industry for years, on all manufacturers’ brands.”


While contractors have made progress, formicary coil corrosion remains a slight concern.

“With tighter homes, coils encountering wetter conditions, and increased volatile organic compounds (VOCs), formicary coil corrosion is still an issue, especially for indoor coil applications such as residential evaporators,” said Ed Rottmann, vice president, sales and product development for Luvata Tubes. “Even though the contributing factors to formicary coil corrosion are on the rise, that doesn’t mean there isn’t a fix for it. There are several solutions available that have been proven effective against formicary corrosion.

“In most cases, leaks in a copper tube coil can be repaired. However, formicary corrosion typically happens quickly, in relative terms to the life of a coil. If all of the contributing factors of formicary corrosion are present, it can occur within a few months. That, combined with multiple leaks in the fin pack area, and especially if there is discoloration seen on the coil, would point to formicary corrosion. We recommend replacing the coil with one that is resistant to formicary corrosion.”

Rottmann noted that some of the solutions for combating formicary corrosion include “an alloy solution found to be at least 25 times more effective against formicary corrosion than the standard DHP (CA122); coating the tube, which is an effective solution against formicary corrosion; aluminum round tube coils; and a full-immersion, factory-applied solution designed to protect HVACR coils from corrosive environments.”

Gaining Ground

If it is an issue, it is a dwindling one, said Tim Fregeau, sales manager, Apex Engineering Products.

“Though formicary coil corrosion continues to be a concern for older or neglected systems, and is more prevalent in certain regions, we haven’t seen it as much in recent years. This is likely due to the heightened awareness of this type of corrosion, improved maintenance practices, and enhanced quality of equipment manufactured throughout the past decade.

“Though different alloys, such as aluminum, have surfaced in the coil market to replace copper (or be used in conjunction with copper), sound maintenance practices and tools are indispensable to prolonging the life of your equipment,” Fregeau said. “This will always be true, regardless if you have regular copper coils, newer microchannel coils, or even coils with protective coatings.”


Regarding microchannel, there continues to be a strong interest in the technology, especially in combating corrosion. Steven Wand, president and CEO of AlCoil, said: “Microchannel coils can deal with corrosion. We have tens of thousands of microchannel coils installed in North America with six years of field experience from 1- to 40-ton coils. When it comes to operational reliability, the microchannel coil has come a long way.”

Jim Bogart, vice president of engineering, AlCoil, noted the thicker tube wall designs use 0.016- to 0.018-inch tube wall thickness and special manufacturing processes “that increase the coil life and significantly minimize corrosion. This is due to the fact that most corrosion (if it occurs) limits its vertical pitting depth and spreads horizontally if the tube wall thickness and material process are right, and therefore should not breach the tube walls.”

Among specific recommendations, Bogart suggested, “In coastal states or high-pollution areas, thin-wall-type microchannel coils should have an epoxy coating or polyurethane coating for protection. These can be applied from the factory or field sprayed onto the coil.” At the same time, thick-wall-type microchannel coils do not need protective coatings in coast or high-pollution areas, and any coating should be optional if the customer desires it or believes it’s needed, he said.

“If a microchannel tube is dinged, knife cut, or breached, the easiest and most effective method of repair is using Red Epoxy, a refrigerant repair product dating back to the 1950s,” said Bogart. “If a thin-wall microchannel coil fails, consider replacement with a thick-wall-type design or replace with an epoxy-coated thin-wall type.”

Brian Baker, owner of Custom Vac Ltd., Winnipeg, Manitoba, Canada, agreed that while the concern remains, it is not what it once was. He said, simply, “We have had failures, but not many.”

Publication date: 6/9/2014

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