The evaporator coil sits inside the indoor unit, behind the filters. Warm room air is drawn across it, gives up its heat to the cold refrigerant inside, and returns to the room cooler and drier. Everything about that process depends on air being able to move freely across the coil.
What clogging does
Filters catch dust, pet hair and lint. As they load up, airflow across the coil drops. Less air means less heat picked up, which means the coil runs colder than designed — and once it falls below freezing, condensate on its surface turns to ice. A coil encased in ice moves no heat at all, so the unit runs continuously, cools nothing, and drips when the ice eventually melts. Owners usually describe this as the aircon leaking water, when the root cause is a filter.
The smell
Coils are permanently damp during operation, and in a humid coastal climate that is ideal for mould and bacteria on the fins and in the blower wheel. That is the source of the sour smell people notice when the unit first starts. No amount of air freshener addresses it; the biofilm has to be physically removed.
What a real clean involves
Filters washed and dried, the coil chemically cleaned and rinsed rather than wiped, the blower wheel cleaned in place or removed, and the drain path flushed. A wipe over the front grille is not a service, whatever it is charged as.
Brands we fit and service
The evaporator coil & filters market splits into hardware built for South African conditions and lookalikes that fail at the first hard season. These are the manufacturers we trust on our installations:
- Split
- midwall
- cassette and ducted indoor units
See our brand guides for how these manufacturers compare.
When the evaporator coil & filters goes wrong
These are the failures we're called to most often — each with its symptoms, causes and our fix on the dedicated problems page:
- Aircon smells musty when it starts up — A sour or damp smell from the indoor unit, strongest in the first minutes after switching on, sometimes with visible dar…
- Indoor unit freezing into a block of ice — Visible ice on the indoor coil behind the filters, weak or no airflow, and water dripping from the unit once it thaws.
Need this fixed or installed?
Our Aircon Cleaning & Sanitising service covers evaporator coil & filters work — from R700, quoted upfront and backed by our 12-month workmanship warranty.