Corrosion of the coil

Although aluminum is ideal for outdoor applications, like any metal exposed to the elements, a condenser coil is susceptible to long-term corrosion. As corrosion begins to deteriorate the composition of the condenser coil, it weakens its integrity, making the fins difficult to straighten through traditional methods. Certain conditions accelerate the corrosion of an outdoor coil, and may include the following:

Proximity to saltwater

When saltwater comes into contact with the metals of a condenser coil, corrosion will be accelerated and pitting will likely occur. This air-borne saltwater can be carried by spray, mist, rain or fog, and can impact systems located more than five miles from the coast. Once the coil has begun to corrode (which can happen very quickly in a harsh coastal environment), it impedes the coil's ability to be easily combed. (Photo: 2)

Industrial and urban areas

During the combustion of coal and fuel oils, sulfur and nitrogen oxides are released. These atmospheric emissions are frequently found in both industrial and urban environments. The particles of these oxides are highly corrosive when they combine with oxygen, water or high humidity conditions, which can lead to corrosion of the metals exposed to these harsh environments. The common placement of HVAC equipment near these emission sites further exacerbates the issue.

Bi-metal coil construction

Galvanic (or bi-metal) corrosion occurs when dissimilar metals come in contact with one another and an electrolyte (such as water). When this condition exists (which it frequently does, due to common coil construction and their outdoor placement), corrosion will be accelerated in the "less noble" of the two metals. Because the aluminum fins in the condenser coil are less noble than the copper tubing contained within, and the coil is frequently wet, electrons freely flow away from the aluminum to the copper, causing the aluminum to degrade over time. (Photo 3)

Sprinkler systems

Water that has a low pH value, low alkalinity, or contains total dissolved solids such as inorganic salts, can accelerate condenser coil corrosion. When untreated water (most often, well water) is used in lawn sprinkler systems, its effect on exposed metal surfaces could be problematic. Condenser coils that are in the path of sprinkler systems using untreated water are subject to the potential of accelerated corrosion. (Photo: 4)

Cleaning agents

Many condenser coil cleaning agents contain sodium hydroxide and are highly caustic. If these agents are not thoroughly rinsed (with neutral pH water) after cleaning the coil, they can deteriorate the aluminum fins quickly. Certain household cleaners, such as bleach, vinegar, and hydrochloric acid are corrosive to aluminum and should not be used. Moreover, some cleaning agents, which may be suitable for aluminum, may not be advised for copper, thus, both metals must be taken into consideration when choosing the appropriate agent.

Special Reports /

Corrosion and hail-damaged HVAC coil repairs

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