There are a few ways in which coils can become compromised. One of the most common is formicary corrosion. Americancoolingandheating.com defines this process as “…a chemical reaction requiring three parts: oxygen, water, and an organic acid. If any of the three parts are removed there can’t be any further formicary corrosion. Formicary corrosion only occurs in copper based alloys.”
Corrosion is most often caused by exposure to fluoride or chloride. Fluoride is present in municipal water supplies and chloride is found in a products including detergents, cleaners, carpeting and fabrics. Pitting occurs when chloride or fluoride ions are transported to the copper metal coils via condensate (water). The ions attack the metal, forming pits that form pinholes, causing the coils to leak refrigerant.
In response, most HVAC manufacturers have switched or are switching the composition of their coils to 100% aluminum.
Craig Sopo 