How to Clean and Maintain a Ductless Mini-Split: What Owners Do and What Technicians Do

What maintenance means on a mini-split

A mini-split is a ductless system. ENERGY STAR says one or more indoor head units are mounted on an interior wall or ceiling, with an accompanying unit outside. It says refrigerant carries the heat directly to the heads inside.

ENERGY STAR calls them ductless heat pumps, or mini split heat pumps, and says they provide both heating and cooling from the same system.

Carrier recommends professional service once a year and says deep cleaning belongs to the pros. Our reading: the upkeep splits into two jobs. The filter and the space around each unit are yours. Deep coil cleaning, clearing a clogged drain, the electrical parts and the refrigerant are a technician's.

Fujitsu's wall-mounted manual 9387602210-02 says the heat exchanger built into the indoor unit has aluminum fins. How the indoor and outdoor units fit together is covered in ductless mini-split systems.

How often to clean the filter: the sources differ

Trane says each indoor unit has a removable air filter that should be cleaned regularly. The sources give different schedules. Fujitsu's manual and Midea's manual for 9,000 to 24,000 BTU split units both say every two weeks. Carrier says every 4 to 6 weeks.

The DOE's Building America Solution Center says to clean ductless heat pump filters every 3 months. ENERGY STAR says heat pump filters should be cleaned when visibly dirty or when the filter light shows. Midea says its indoor unit flashes CL after 240 hours of use as a reminder to clean the filter.

Midea also says maintenance intervals may vary with the installation environment, such as dusty zones. Trane says to clean the filters more often if your family is sensitive to dust or has pets. Our reading: start with the schedule in your own owner's manual, and check the filter sooner if it fills up faster.

The reason to clean the filter is airflow. Fujitsu says dirt on the filter reduces airflow, lowers operating efficiency and raises the noise. Midea says dirty filters can cause reduced cooling, intermittent operation, frost on the indoor coil or blown fuses. The DOE guide says that in some cases a clogged filter can make the unit shut off until the filter is cleaned.

How the manuals say to clean a filter

Turn the unit off first. The DOE guide says you can do that at the thermostat or with the remote. Fujitsu and Midea also say to disconnect the power supply before cleaning.

The DOE guide says most wall-mounted units have a hinged front panel that lifts out and up, and that the filters are usually just below the cover. On some models, it says, the filters sit on top of the unit and are held by magnets. Your manual shows where yours are.

Take the filter down to the floor to clean it, as the DOE guide advises. It says to vacuum the dust off with a brush attachment. If the filter is sticky or discolored, it says, wash it in warm soapy water. Fujitsu and Midea both call for a mild detergent.

Dry the filter fully before it goes back. Fujitsu says to dry the filters thoroughly in shade. Midea says to keep the filter out of direct sunlight, because sunlight can shrink it. Fujitsu says to always operate the unit with the air filters installed.

Mind the ladder. Fujitsu says not to stand on slippery, uneven or unstable surfaces when you maintain the unit. It says that if filter cleaning involves high-place work, you should consult authorized service personnel. Our reading: a unit mounted high on a wall or over a stairwell is a fair job to hand to a technician.

Wiping the cabinet and keeping space clear

Carrier says to wipe the indoor cabinet with a dry cloth or small vacuum to prevent dust buildup. Midea says to use only a soft, dry cloth, or a cloth soaked in warm water if the unit is especially dirty. It says not to use chemicals or chemically treated cloths.

Fujitsu says not to use water hotter than 104°F (40°C) on the indoor unit body. It also rules out scouring cleanser and solvents such as benzene or thinner.

Keep water and sprays out of the inside. Midea says not to use water to clean the inside of the indoor unit, because it can destroy insulation and cause electrical shock. Fujitsu says not to expose the indoor unit to liquid insecticides or hair sprays. Do not touch the metal inside either. Midea says its sharp metal edges can cut you.

Give each unit room. Trane says not to put bookcases, picture frames or other furniture close to an indoor unit. Fujitsu says to keep the area around the outdoor unit clean and tidy, with nothing placed around it. Carrier says to clear leaves, grass clippings and debris from the outdoor base and keep shrubs trimmed back.

Midea says any maintenance and cleaning of the outdoor unit should be performed by a dealer Midea has authorized or a licensed service provider. Our reading: follow your own manual, and if it says nothing, leave the outdoor coil to the technician. If the outdoor unit sits near salt water, see coastal coil protection.

What a technician's visit covers

Carrier says a thorough professional inspection typically includes deep cleaning the evaporator and condensing coils with specialized solutions, to remove hidden mold or buildup. Midea calls the outdoor unit the outdoor condensing unit. Trane calls the indoor units evaporator units.

Carrier says the inspection typically also includes inspecting the refrigerant lines, the mounting hardware and the electrical connections, and checking for refrigerant leaks. It also lists applying fungistats, which Carrier describes as treatments to discourage future biological growth on coils.

Trane's dealer list adds a spot-check of the electrical connections inside the outdoor unit for loose connections or overheating. It also covers the run capacitors for bulging, deformation or leaks. Trane says refrigerant leaks are especially common at flare connections. It says the hose that carries water away from the indoor units should be checked so water flows freely.

Fujitsu says that after a long period of use, dust inside the indoor unit may reduce performance even if you have maintained the unit properly. In that case it recommends a product inspection and says to consult authorized service personnel for more information.

On timing, Carrier says at least once a year. Trane says twice a year, once before heating season and again before cooling season. This work involves refrigerant and electrical parts, so it is for a licensed contractor, and this page gives no steps for it.

What is different in Florida: water, humidity and an empty house

Midea says that in cooling mode the system cools, dries and filters the room air. The water it removes, called condensate, drains through a hose, which Trane says should be checked so water flows freely. Fujitsu says that if the unit runs continuously for many hours, water may condense on the surface and drip.

The National Weather Service Tampa Bay office says the rainy season typically brings persistent dew point values above 70°F. It dates that season May 25 to October 10 for West Central Florida, apart from Southwest Florida.

The EPA says to keep air conditioning drip pans clean and the drain lines unobstructed and flowing properly. Trane says water leaks can mean the drain line or pan is clogged or over-filled.

Our reading: water on the wall or floor under an indoor unit is a reason to call. Carrier lists water leaking from the indoor unit among the signs to contact a Carrier expert for repair. It says a professional technician is best equipped to clear clogs safely. Air conditioner leaking water explains how condensate leaves a system.

If the house will sit closed up for a while, the manuals give a drying step. Before an extended shutdown, Midea says to clean the filters and run the unit in fan-only mode for 12 hours to dry the internal parts. Fujitsu says that after the unit has been off for a month or more, run Fan mode for half a day before normal use.

The EPA also says not to run an HVAC system if you know or suspect that it is contaminated with mold. If you see mold inside a unit, leave it off and call a technician. Mold in HVAC systems in Florida covers that problem in more depth.