'Wet socks' smell from a Daikin, 8 years old, Drumul Taberei
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Hi. I have a 9,000 BTU Daikin in the bedroom, 10-storey block on Brașov street in Drumul Taberei. It works perfectly, cools, does not drip, but for two summers now it has had a sour smell, exactly like wet socks left in a gym bag. It is not the classic mould smell, it is something sharper. I sprayed an AC cleaning spray from the DIY store into the grille and it was worse for a week. What is that smell actually?
What is really happening
Bacterial colonies settle on the aluminium of the evaporator – most often Methylobacterium, a bacterium resistant to drying and temperature shocks – and produce volatile fatty acids, the same ones behind sweat odour. An 8-year-old Daikin used in a bedroom at night is exactly the profile: hours of condensation, then shut-off in the morning with wet fins, in a closed room. The 'sharper than mould' character comes from those bacterial compounds, not from spores. Consumer sprays reach the first 2–3 cm of the fins; the biofilm clings to the whole coil, including the back and the fan roller.
- Deposits or moisture inside the unit.
- The condensate drainage route.
- Sources within the room, assessed separately.
- Dense bacterial biofilm (~11,000–47,000 CFU/cm²) dominated by Methylobacterium forms on aluminium heat exchangers. [Current Microbiology / PubMed Central, 2012]
- Methylobacterium, the dominant bacterium in evaporator biofilm, is a strong biofilm former resistant to UV, desiccation and heat/cold shock. [mSphere (ASM) / PubMed Central, 2020]
- The 'dirty sock' or musty smell from an air conditioner comes from volatile organic compounds produced by microbial biofilm on the evaporator and blower. [Current Microbiology, 2000]
- EPA principle: mould must be physically removed, not merely 'killed'; biocides are not recommended as routine practice. [US EPA, 2024]
What we do on site
- We test the smell at start-up together with you, then open the unit and photograph the evaporator and roller – we want you to see what we are cleaning.
- Sealed collection bag under the unit; bed and nightstands covered with film.
- Alkaline cleaning solution over the full depth of the evaporator and on the roller, 5–10 minutes' contact time.
- Pressure wash, in place, no dismantling; the black water running into the bag is exactly the biofilm that smelled.
- Sanitising solution on the cleaned surfaces, including the drain pan and drain hose.
- We also wash the outdoor unit on the 7th-floor balcony – at 8 years its fins are packed with dust.
- We run 'Cool', then 'Fan', and confirm the air comes out neutral. See current rates on the Prices page.
What you can do yourself
- Set a timer: unit on 'Fan' for the last 30 minutes before you wake up, so the fins dry before shut-off.
- Raise the set temperature to 25–26 °C – less condensate, slower biofilm.
- Filters: warm water and a drop of dish soap every two weeks.
What NOT to do
- Stop using the store cleaning spray – it does not reach where it matters and leaves sticky residue that catches dust.
- Do not spray perfume or essential oil into the grille – oil feeds bacteria.
- Do not pour vinegar or bleach into the pan 'to disinfect' – vinegar corrodes aluminium, bleach ends up in your lungs.
Prevention
A bedroom is the harshest regime for a unit: 8 hours of condensation a night in a closed room. Annual sanitising is a must, plus daily drying on 'Fan' – with that, the sock smell does not return between visits.
When to call us
When the smell has been there two summers already, there is nothing left to wait for: 0764 012 943, Monday–Saturday 08:00–20:00. Drumul Taberei is on our patch, we schedule quickly.
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Read also
- Bad smell from the air conditioner
- The air we breathe at home
- Symptoms of an uncleaned air conditioner
Sources (7)
- pmc.ncbi.nlm.nih.gov/articles/PMC3378845/
- pmc.ncbi.nlm.nih.gov/articles/PMC6968652/
- link.springer.com/article/10.1007/s002840010120
- link.springer.com/article/10.1007/s002849900435
- www.epa.gov/mold/mold-remediation-schools-and-commercial-buildings-guide-chapter-3
- www.epa.gov/mold/brief-guide-mold-moisture-and-your-home
- www.epa.gov/indoor-air-quality-iaq/should-you-have-air-ducts-your-home-cleaned
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.