If your mini-split smells musty, blows weaker than it used to, or shows dark spots around the vents, the problem is usually inside the unit, not on the filter. Here is why it happens, what to look for, and how often it should be cleaned.
Why mini-splits get moldy
Cooling makes water. As a mini-split cools the air, moisture condenses on the indoor coil and runs down into the drain pan. The blower wheel sits in that damp air the whole time. When the unit shuts off, the inside stays warm and wet, and dust and lint settle on every surface. Mildew grows where it is damp, dark and dusty, and the inside of an indoor unit has all three.
It builds faster in NYC summers, in kitchens and restaurants where grease and humidity are in the air, and in units that run all day.
Signs your mini-split needs a cleaning
A musty or sour smell when the unit starts
Dark specks or residue on the louvers and air outlet
Weaker airflow, or the room takes longer to cool
Water dripping from the indoor unit
Visible buildup on the blower wheel
Why rinsing the filter is not enough
Filters catch part of the dust, but the buildup that causes odors collects on the coil, the blower wheel and the drain pan behind the cover. A clogged drain pan or line can also leak water onto walls and floors.
How often should a mini-split be cleaned?
As a rule of thumb, homes should plan on a deep cleaning about once a year. Units that run most of the day, or that sit in kitchens, bars, restaurants and busy offices, do better with cleaning twice a year. For commercial spaces and multi-unit buildings, we recommend quarterly or semi-annual planned maintenance.
What a deep cleaning looks like
Here is the process we follow, start to finish: inspect the unit, remove the blower wheel and drain pan, wash the parts, protect the unit and the area around it, treat the coil and drain pan, then reassemble and test.
Maintaining several units?
If you manage a building or business with 5 or more units, we offer a free walk-through and a written proposal. Call (646) 946-5584 or email office@jllmechanical.com.
JLL Mechanical Inc. provides mini-split, VRF, PTAC and console service across all five NYC boroughs.
Sources: EPA, A Brief Guide to Mold, Moisture and Your Home; Energy Vanguard, Ductless Mini-Splits Can Get Nasty Inside.