A mini-split, ductless AC system requires some regular maintenance, just like a conventional AC unit. Perform annual cleaning chores either in fall, after shutting down the system for the winter, or in spring before you turn it on for the first time for the season. Monthly tasks can be done at any time of the month, but try and make it a consistent time so you don't forget.
The cooling coil is located in the exterior cabinet of the system. Before cleaning, turn off all the indoor air handling units, along with the main circuit to the exterior cabinet. This is to ensure that there is no electric shock danger. Allow the unit to cool for an hour or longer so you don't hurt yourself on any warm components.
You need a soft, lint-free cloth to properly clean the coil. Begin by first clearing any debris, such as leaves, away from the cabinet. Then, remove the screws that hold the cabinet cover in place and lift the cover off. Run the cloth over the coils to remove any dust or debris.
Take a few minutes to fully inspect the coils. There should be no signs of mold or discoloration on the coils, since this can indicate a moisture issue inside the cabinet. Replace the cabinet cover once you are done. If you notice mold, do not try to clean it off. Instead, call in an HVAC technician so they can both clean the coils more thoroughly and inspect the unit to make sure there are no leaks.
Monthly maintenance primarily consists of cleaning the filter. Most mini-split systems have reusable filters, so they are cleaned rather than replaced, during the cooling system.
Turn off and cool down the unit as you would for annual maintenance. Then, remove the filter from the unit. It is usually located on the wall-mounted air exchange unit inside the home. Removal methods depend on your unit, it may simply slide out or you may need to unlatch it. Wipe the filter clean with a a lint-free cloth. Some filters are designed to be rinse clean with water – these must dry completely before you place them back inside the unit.
Once the filter is clean, dry and replaced, take a few minutes to dust the air handling units. This not only keeps them looking good, it also gives you a chance to inspect each to make sure there are no visible issues with the units. If you notice any problems or have trouble maintaining the mini-split system on your own, contact an air conditioning repair tech in your area.