The outdoor AC unit is designed for exposure to the elements, and it’s subject to considerable wear and tear over the years. Heating and cooling equipment needs regular maintenance to perform efficiently. During an annual maintenance visit, the HVAC technician will check for signs of rust and other potential problems. When the AC unit is poorly maintained and the moisture content is high there are likely to be corrosion issues. In this article, we will take a closer look at AC units and explain how you can deal with a corrosion problem.

Is This a Serious Problem?

Yes, a rusty AC unit looks ugly, but the problems go far beyond mere aesthetic appeal. Corrosion affects how the air conditioning functions in fundamental ways. When the AC unit is rusty, it takes longer to heat or cool the home and this drives up the energy bills. If the rust is ignored, it will spread, and components will be damaged. This will lead to an unexpected repair bill, premature failure, and a shorter than expected lifespan.

4 Common Causes of AC Unit Corrosion

The formation of rust on steel, iron, and other metal surfaces is caused by the exposure to oxygen and water during certain time periods. When corrosion begins, it tends to spread quickly, and the metal surface is damaged. The AC components that are most at risk include air filters, the coils, the drain pan, refrigerant lines, fan blades, the compressor, and the ductwork system. Let’s take a look at four common causes of AC unit corrosion:

1.   Excessive Moisture Levels

Moisture is the most common cause of rust, the source can be rain, condensation, or humid air. The air conditioner removes moisture from the home and condenses it on the evaporator coils. The moisture is then dripped down into the drain pan and from there out into the drain. This process is an essential part of the design, but if the moisture stays in contact with the equipment for a prolonged period of time, it will cause problems. Excessive moisture occurs when the drain pan is not draining properly and this usually happens when there is a clog in the system. This can lead to water overflowing problems and the AC components can be damaged. If the AC unit is in close proximity to plants, they can be corroded by chemical fertilizers. When rain falls directly on the AC unit, this will accelerate the corrosion process.

2.   Insufficient Maintenance

The AC filter can remove airborne contaminants from the air, but moisture can build up in a dirty filter, and this, mixed with debris, can lead to the formation of rust. When the filters are dirty, they can cause corrosion in the coils. The outdoor AC units are prone to intrusion from dirt, dust, twigs, leaves, and other organic debris. These may collect in the condenser unit, and this will degrade the performance. The drain system can be clogged, and high levels of trapped moisture may lead to rust formation.

3.   An Aging AC System

Air conditioner systems have a lifespan of 10-15 years, and regular maintenance will place the system at the upper end of that range. Corrosion is a normal aspect of aging in any piece of equipment with metal components and cases. As the AC system ages, it will degrade in performance and efficiency. Some signs of an aging system include a lack of airflow, strange noises, frequent repairs, high energy bills, and more.

4.   Volatile Organic Compounds (VOCs)

These chemical compounds are found in certain items, such as paints, household cleaners, air fresheners, and more. If VOCs are present in your air, they will enter the AC system when it draws in air to remove the heat. Gradually, VOCs will corrode the copper refrigerant pipes, which can lead to leaks that degrade the performance of the AC system.

Removing Rust from the Outdoor AC Unit

If you catch the corrosion early, it may be possible to remove the rust yourself. Turn off the AC system circuit breaker, use a circuit tester to ensure that there is no power, and remove the outdoor unit side cover with a screwdriver. The AC unit manual will show you the screw locations for your specific make and model. Remove the outdoor unit cover; it may be heavy, and you may need a second person to help you.

The AC condenser unit is now exposed. It’s a square or rectangular panel that has coils and fins protruding from it. The condenser may be covered with light rust, and this can be removed with a condenser coil spray. Cover the coils with the spray, and it will foam up on the rust to loosen it for removal. Any rust left on the coil surfaces can be removed with a soft nylon brush. Use a gentle scrubbing action to prevent damage to the condenser coils.

Excess coil spray will drip into the drain pan, which must be free of clogs as a preventative measure. The drain pan can be cleaned with a 1:1 mix of bleach and water, which is run into the drain pan. To protect the AC outdoor unit, you should remove any nearby vegetation and outdoor items that may be stored in the area. The exposed surfaces can be cleaned with a rust-proof primer and then painted. When you’re done, reassemble the outdoor AC unit, restore the power and test it to ensure that it’s working.

In Conclusion

The formation of rust on metal surfaces will gradually degrade the AC unit. Keeping the air filters clean, dealing with drain line clogs, and trimming back vegetation will all help to prevent corrosion. But, the best way to protect your air conditioning system is to invest in regular HVAC maintenance. The HVAC technician can identify many potential problems at an earlier stage when they are less expensive to fix. If you need essential maintenance for your AC system, contact your local heating and cooling specialist today.