Maintenance Tips for Ductless (Mini-Split) Air Conditioners

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A ductless, or mini-split, air conditioner is a great solution for people who want to cool one room in their house without having to cool the whole house. It's also a great way to add air conditioning to an older house that's heated by a boiler and radiators without an existing system of forced-air heat ducts.


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Ductless Air Conditioner Basics

A mini-split does essentially the same job a a window air conditioner, but you can install it on a wall. It's connected directly to the compressor, which is situated outside. This arrangement provides a number of advantages over other air conditioning systems, including:


  • Less noise, because the working part of the system is outside.
  • Less chance of leakage and more cooling per watt, because there are no ducts, which waste up to 30 percent of the system's efficiency.
  • Cool air exactly where you need it, and more control over temperature.
  • Better air quality, because ductless systems have highly efficient filtration systems.
  • Lower installation costs than central air conditioning, although the cost of the air conditioner is more than that of a window unit.


Ductless systems aren't just for cooling. You can choose a ductless heat pump system that provides cool air in the summer and warm air in the winter, so you can enjoy improved air quality throughout the year. However, these systems may not be sufficient to supply the full heating needs in very cold climates, as some cease to offer adequate heating when temperatures fall below freezing.


Because of the extensive filtration system, a ductless air system requires more maintenance than a conventional one. You don't have to worry about cleaning the ducts, because there aren't any, but you do have to clean the filters in the indoor unit, as well as the coils and the casing. The outdoor compressor unit also needs regular cleaning and maintenance.


Cleaning the Indoor Unit

The air handler is enclosed within the sleek, rectangular indoor portion of a ductless system, which also houses the evaporative coils that suck heat from the room air and replace it with cool air. Cleaning the filters is key to efficient cooling and maintaining an ample supply of healthy, breathable air.


Most systems have an array of filters. The main filters remove large, particulate matter from the air while the HEPA filters, which are situated behind the main ones, deal with microscopic particles and microorganisms, such as mold spores and pollen. The indoor unit needs needs maintenance, on average, about once a month.

  1. Turn off the power​ and unplug the unit before servicing it. If the unit is hardwired into the home circuitry, turn off the circuit breaker that controls it. This safety precaution ensures the compressor won't come on while you're working, which is dangerous for both you and the unit.
  2. Open the cover and remove the filters.​ Pull the smaller HEPA filters off the larger particulate filters and clean them with detergent and water. Rinse thoroughly and let them dry. Clean the larger filters by holding them under running water and brushing lightly with a sponge or soft brush. Check the conditions of the filters and replace if necessary. The HEPA filters in particular need to be replaced every 12 to 18 months.
  3. Clean the evaporative coils.​ The best way to do this is to use a commercial spray cleaner. Rinse lightly by spraying clean water from a spray bottle, holding a small bucket or plastic bag under the unit to catch runoff. To prevent mold growth, it's a good idea to follow up by spraying the coils with a mildewcide/bacteriostatic.
  4. Replace the filters and close the cover.​ Let the coils and all the filters dry thoroughly first.



Consult your owner's manual for any extra service your unit might need. Some systems use negative ion generators and other technologies for purifying air, and the manual should detail the cleaning procedure for these components.

Cleaning the Outdoor Unit

Part of air conditioning maintenance is cleaning the outdoor components. The outdoor unit contains the compressor pump and the condenser coils where the refrigerant is forced into the liquid state under pressure prior to circulating through the evaporative coils. This process generates heat, and it's important for the heat to be able to escape, or the pump can overheat and stop working.


  1. Clean the fins​ on the housing grate with a damp rag or by spray them with high-pressure water from a garden hose. Too much pressure can do damage to fins.
  2. Open the cover​ to expose the pump and coils and clean off dust by sucking it with a wet/dry vacuum cleaner or blowing it off with a leaf blower.
  3. Deep-clean the coils​ periodically by washing them with a hose. For best results, replace the hose nozzle with a needle sprayer specifically designed for cleaning condenser coils. You can also use the jet function on a conventional multi-setting nozzle.
  4. Give the fan blades a quick turn​ to make sure the fan isn't loose or unbalanced. If the fan has any lateral movement, have it serviced by an HVAC pro.

Ductless Air Conditioner Troubleshooting Tips

Ductless systems almost always come with a remote, and if the remote stops operating the unit, the first thing to do is to test the batteries in the remote and change them if necessary. Next, make sure that the unit is plugged in and that the outlet has power. Sometimes the cause of a power failure in one room is a tripped GFCI outlet in another room, and sometimes it's a tripped circuit breaker in the main service panel.

Troubleshooting poor cooling is similar to troubleshooting a regular air conditioner. If a unit is blowing air, but the air isn't cold, go outside and make sure the compressor is running. You should also clean the filters in the indoor unit, because there may not be enough circulation around the evaporative coils. A loss of cooling power often indicates a refrigerant leak, and that, along with a malfunctioning compressor, are jobs for an HVAC professional licensed to do repairs on refrigeration systems.

Other malfunctions, such as intermittent operation or failure of the unit to come on when there are no issues with the remote or the power, are usually accompanied by an error code on the LED display. Your user's manual contains a list of these codes. If you can't find the manual, you can usually find an online version on the manufacturer's website.