How to clean AC condenser coils, and which cleaners to avoid

What the condenser coil does and why dirt matters

Carrier says the condenser coil, found in the outdoor unit, releases the heat the system captured indoors. Refrigerant flows through the coils. Carrier says most coils are made of copper tubing that runs through a series of thin aluminum strips called fins.

The University of Illinois System's EnergySense center explains the parts the same way. It says the fins disperse heat, and fans pass air across the fins and coils to speed up cooling. It also says a blanket of dirt and dust will insulate the coils, preventing heat dispersion and blocking airflow through the fins. The result, it says, is that the compressor runs more than it otherwise would. It says the compressor, typically located outside the building, raises the heat of the refrigerant so the condensing unit can reject it.

The DOE's 2013 Building America guideline was written for contractors. It says dust, lint, leaves, grass clippings and other debris can be sucked into the fins as the fan draws air through them. It says these obstructions lower the coil's effectiveness and reduce cooling efficiency. The ENERGY STAR maintenance checklist says dirty coils reduce the system's ability to cool your home and cause the system to run longer.

What you can do without opening the unit

Trane says you can help keep the condenser coil cleaner by keeping plants and debris away from the unit and off of it. It says to keep landscaping plants trimmed to at least two feet away from the unit on all sides. Trane also says to mow so that a side-discharge mower throws grass away from the unit. It adds that you should remove leaves and twigs that land on the top of the unit.

The UF/IFAS Extension, the University of Florida's extension service, adds, on where the unit is placed, that a clothes dryer should not be vented within 10 feet of the outdoor unit. Its reason is that dryer lint will cling to the condensing coil.

Trane describes gently spraying the coil from the outside with a garden hose, and Carrier says a gentle garden hose spray is the safest way to rinse the outdoor unit. Trane warns not to use the jet setting or a power washer, because the force of the water can bend or damage the fins. Bryant says to turn off the power before performing any coil maintenance. It also says water should stay off electrical components. Our reading: because even a rinse starts with shutting off power, leave the rinse to a technician too.

How a technician cleans the coil

Trane's guidance says a professional will turn off the unit and assess all the components, including the condenser coil. It says they may use compressed air to blow away loose debris. Depending on how dirty the coil is, Trane says they may also use a mild detergent or a chemical cleaner. That cleaner goes on with a low-pressure sprayer or an aerosol can.

Carrier says the outdoor coil usually wraps around the inner parts and acts as the side walls of the unit. In some cases, it says, the outer casing and top may need to be removed. When a technician uses compressed air, Carrier says it is blown opposite the normal direction of airflow. It is also aimed straight through the fins, not at an angle, because the fins bend easily.

The DOE guideline's own steps include shutting off the system and pulling the fuse that powers the outdoor unit. It then has the technician remove the top of the unit's casing, where the fan motor is sometimes attached. These steps involve the fuse that powers the outdoor unit and the fan motor's wires. This page gives no steps for them.

The same guideline notes that some two-row coils are bent into a U shape, and dirt clogs between the rows. It says separating those coils for cleaning requires the skills of a qualified HVAC technician. Trane puts the general point plainly: AC coil maintenance is dangerous and should only be handled by a licensed HVAC technician.

Which coil cleaner is safe

There is no single product answer, and the makers we read do not fully agree.

Carrier says acidic cleaners damage the copper and alloy metals used in the coil. It says they can also cause corrosion that will shorten the life of the coil. Bryant says to avoid harsh chemicals such as bleach or ammonia, because they can damage the coils and nearby parts. Bryant also rules out wire brushes, steel wool and solvents.

Household detergent is where the makers split. Carrier describes a technician using a solution of mild household detergent and water, applied with a low-pressure sprayer. Trane describes a technician using a low-acidity household dish detergent mixed with warm water. Bryant's own FAQ disagrees. It says to avoid standard household cleaners, because they can cause corrosion, and to use a dedicated, non-acidic foaming coil cleaner.

Bryant says cleaner formulations and application requirements vary, so do not assume one cleaner or dilution is right for every coil. A 2015 Goodman service bulletin found that cleaners containing chlorine can harm the aluminum-tube indoor coils in its equipment. That bulletin covered indoor coils only.

The University of Illinois page offers a calmer rule. When a coil is regularly maintained, it says, water should be all that is necessary. When soap or chemicals are needed, it says to choose the gentlest one possible and follow the maker's instructions. It also says to rinse any leftover chemical off the coil.

Water pressure and the fins

Carrier says damaged or bent fins can restrict airflow and reduce heat transfer.

Carrier says a contractor should never use a pressure washer, because the high-powered spray will most likely damage the coil's thin metal fins. Bryant gives the same warning, saying high-pressure water can bend or break the delicate fins. The University of Illinois page goes further. It warns against a hard stream from a garden hose too, and suggests a mist or rain setting instead.

One source is less strict. The DOE guideline, written for contractors and technicians, allows a pressure washer if the stream is not so powerful that it bends or damages the fins. Our reading: the equipment makers' own pages rule pressure washers out, so they are not worth the risk on a home unit.

Bent fins can be straightened, but only with care. Trane says a technician who notices bent fins will straighten them with a special tool, and Carrier says service may include this. The University of Illinois page says fins may be straightened, but care must be used to avoid permanent damage. The DOE guideline lists a damaged condenser coil, with fins compressed or corroded, among the signs that the outdoor unit may need replacing.

How often to have the coil checked

The UF/IFAS Extension says the outdoor coil must be checked periodically for dirt buildup and cleaned if necessary. It calls dirt on the indoor coil the single most common cause of poor efficiency. Trane says the evaporator coil, inside the indoor unit, absorbs heat and humidity from your home. Our guide to the evaporator coil covers that side. Trane says regular maintenance can help a unit last longer, even if you run it nearly year-round.

Carrier says coils should be cleaned when they are dirty. How fast that happens, it says, depends on how often you run the system, your filter and the dust around your home. Carrier recommends a professional maintenance check at least once a year, before summer. Trane recommends a tune-up every spring, and the ENERGY STAR checklist lists cleaning both coils in a contractor's check-up.

Trane also says changing the filter helps keep dirt off the coils, which HVAC air filters explains. For coastal salt, see coastal coil protection. For the whole yearly list, see the Florida AC maintenance checklist.