HVAC Basics: AC Coil Cleaning

AC coil cleaning is an important HVAC preventative maintenance task. Taking care of these critical system components improves system efficiency, cooling effectiveness, and helps to prevent breakdowns. 

Many HVAC service companies include coil cleaning in preventative maintenance service. In some cases, it may be offered as an add-on service for customers who might not need coil cleaning as often as they need other maintenance services.

Here’s a primer for HVAC technicians-in-training about the benefits of regular AC coil cleaning, as well as the basics for performing the procedure.

What do air conditioning coils do?

If you’re just getting started, you might not yet understand the importance of AC coils and their role in the cooling process. A common split air conditioning system has two types of coils: evaporator coils and condenser coils. Here’s a simple explanation of the role of each type of coil.

EVAPORATOR COILS are located on the air intake side of the air handler unit, which is typically located indoors (or sometimes on the roof in a packaged rooftop system). The evaporator coil’s job is to remove heat from indoor air, which is why it’s sometimes called the cooling coil. The coil absorbs heat in the form of moisture, allowing the blower fan to blow cooled air into the space.

CONDENSER COILS are located in the condenser/compressor unit, which is typically located outside (or sometimes in a mechanical room with access to outdoor air). The condenser coil’s job is to release heat from the system to the outside. The condenser fan blows air across the coils to cool them and facilitate the transfer of heat.

This process is facilitated by the refrigeration cycle, which you can read about here.

You can easily recognize the evaporator and condenser coils when you look at an air conditioning system. They consist of coiled tubing (usually copper) running through strips of aluminum called fins, which help with heat transfer. 

Why regular AC coil cleaning is essential

Now that you understand the important job that the coils need to do, it’s easy to understand why they need regular cleaning. When the copper tubes and fins get coated in dirt, grime, and other contaminants, that impedes the coil’s ability to absorb or release heat.

When heat transfer slows down, the system has a harder time reaching set temperature, and your customer may notice reduced cooling. They may also notice higher energy bills, because the system is running longer and working harder in an effort to cool the space. That also causes more wear and tear on the parts, so the system may have problems with belts, fans, and other components.

Over time, grime on the coils can cause corrosion of the pipes, leading to refrigerant leaks that further reduce cooling performance.

Another risk from dirty coils is system overheating, which can lead to compressor failure. That can happen when the condenser coils can no longer release heat effectively.

The condenser coil is particularly susceptible to the adverse effects of weather, dirt, soot and other outside pollutants. Here in the New York City area, AC coils can get grungy very quickly.

Both types of AC coils have fins which can be easily damaged, so it’s important to know the right way to perform AC coil cleaning. 

AC coil cleaning: Step by step

IMPORTANT: Before you begin, be sure to turn off the system and disable the breaker to cut power to the unit. Also, be sure to protect yourself with proper PPE, including safety goggles and gloves.

Basic steps to clean condenser coils:

1. Remove protective covers from the unit.

2. Depending on the model’s design, you will probably need to unscrew and move the condenser fan assembly so you can access the coil.

3. Remove large debris like leaves from the grill and the inside of the unit, then use a shop vac to remove the remaining accumulated dirt.

4. If any of the coil’s fins are bent, use a fin comb to carefully straighten them. (Avoid touching the coils or fins with your hands to prevent damage.)

5. Spray the fins and cabinet interior with coil cleaning foam, and let it sit for 10 minutes. (Always use cleaners designed for coil cleaning, and never use anything corrosive.)

6. Using a garden hose with a spray attachment, carefully rinse the cleaner from the coils and the inside of the cabinet. Don’t use too much water pressure to prevent damaging the fins. Start at the top on one side and work your way down, then do the other side. 

7. Once the unit is completely dry, replace the fan assembly and put the protective covers back on.

Basic steps to clean evaporator coils:

1. Open the access door to the indoor unit and locate the evaporator coil on the supply side (it’s often shaped like the letter A). 

2. Since they aren’t exposed to the outdoors, evaporator coils may not be as dirty as the condenser coils. However, you’ll likely see a buildup on the inner side of the coil.

3. Using a nylon brush, carefully brush away dirt from the fins, starting at the top and working your way down.

4. Use your shop vac as needed to clean up the debris you brush away from the fins.

5. If any of the coil’s fins are bent, use a fin comb to carefully straighten them. (Avoid touching the coils or fins with your hands to prevent damage.)

6. Spray the evaporator coil assembly with coil cleaning foam, and let sit for about 5 minutes. (Always use cleaners designed for coil cleaning, and never use anything corrosive.)

7. Since the evaporator coil is indoors, you won’t be able to spray with a hose to remove the foam and debris. Instead, rinse with water in a spray bottle, using as little water as you can. As you work, clean up the water with your shop vac.

8. You might have to spray with foam and rinse several times to remove all the debris. 

9. Once the unit is completely dry, reassemble and replace the access door.

This gives you a basic understanding of what’s involved in AC coil cleaning. Remember that every unit is different, so always follow the process you’re taught by your employer. 

More HVAC Basics for technicians in training

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