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I wash the filters monthly – does that mean the unit is clean?

Editorial guide · Updated 18 September 2026

In short Short answer: clean filters are the best thing you can do and slow fouling a lot, but they do not stop biofilm – it grows on the wet evaporator and the fan roller, behind the filters, from moisture rather than dust. At 5 years without an internal wash, your unit is almost certainly coated with a film you cannot see from the filter level.

This page explains a situation in an editorial format. It is not an open discussion board or a verified customer review. Contact us on WhatsApp about your own appliance.

Situation discussed

Block in Colentina, 2-room flat, 12,000 BTU Gree in the living room, 5 years old. I am very disciplined: I wash the filters monthly, sometimes every two weeks. No smell (or I do not notice one). Friends say it needs 'professional cleaning' anyway. Isn't that an exaggeration, if the filters are always clean?

Editorial explanation · Revizie AC

What is really happening

The filter retains coarse dust; fine particles and spores pass through and settle on the cold fins, where surface humidity stays above 80% for as long as the unit cools – exactly the threshold above which mould grows. Research on split units shows the cross-flow fan is more contaminated than the filter and than the face of the evaporator, i.e. precisely where filter washing cannot reach. 'Not noticing' is relative: the nose adapts to one's own home, while guests smell it from the door.

Explanatory diagramIndoor unit components
Indoor unit components
  1. Filters retain some airborne particles.
  2. The coil transfers heat; during cooling it can collect condensate.
  3. The blower moves air.
  4. The pan collects condensate for drainage.
What the studies say
  • Daikin, Mitsubishi Electric, LG and Panasonic recommend cleaning the indoor unit's dust filters every 2 weeks. [Daikin, 2023]
  • Filter efficiency and indoor particle concentration are the most important factors determining how fast the evaporator fouls. [Lawrence Berkeley National Laboratory / , 2002]
  • Mould does not grow below roughly 80% surface relative humidity, but the cold surfaces inside an air conditioner constantly exceed this threshold. [WHO / NCBI Bookshelf, 2009]
  • The blower (cross-flow fan) is the most fungus-contaminated component of a split unit, more than the filter or the front of the evaporator. [Indoor Air, 2023]

What we do on site

  1. We take out the filters (and praise them, they are clean) and show you the roller and the back of the evaporator with a torch – usually the 'aha' moment.
  2. Double waterproof cover sealed to the wall, hose to the bucket, foil on the floor.
  3. Alkaline solution on the evaporator and roller, contact time, adjustable pressure wash in place; pan and condensate hose flushed until clear.
  4. Sanitising on the clean surfaces; outdoor unit washed in place.
  5. Drying on 'Fan', test, bucket with clear rinse water. See current rates on the Prices page.

What you can do yourself

  • Keep going with the filters – you are in the top 5% of customers.
  • Add 20–30 minutes on 'Fan' after each evening of cooling; it dries the evaporator and slows the biofilm.
  • Ask a guest to tell you honestly whether it smells at start-up.

What NOT to do

  • Do not try to scrub the evaporator with a sponge through the filter opening – you bend the fins and never reach the roller.

Prevention

With your impeccable filters, one internal clean a year is enough and the unit will probably outlast the average by far.

When to call us

0764 012 943, Monday–Saturday 08:00–20:00, WhatsApp; Colentina is 20 minutes away.

Technician washing the air conditioner inside the cover with a pressure pump in a white living room
Technician washing the air conditioner inside the cover with a pressure pump in a white living room
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The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.