After renovation, the unit blows white dust and cools poorly – needs cleaning or is it broken?
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.
I renovated my flat in Băneasa (plastering, sanding, painting) and, although I covered the unit with film, after the renovation the 12,000 BTU Mitsubishi blows fine white dust and cools noticeably worse. It is only 2 years old. The workers switched it on a few times 'because it was hot'. Is it broken?
What is really happening
Plaster and sanding dust is the worst dirt for a split: the particles are smaller than the filter mesh, and on the cold, wet fins they turn into a mineral layer that blocks airflow and heat transfer. Filter efficiency and the room's particle concentration are the two factors that set how fast the evaporator fouls, and a building site upends both. Also, this dust is a perfect substrate for biofilm, so if it is not removed now, by summer you will have a smell too.
- Filters retain some airborne particles.
- The coil transfers heat; during cooling it can collect condensate.
- The blower moves air.
- The pan collects condensate for drainage.
- Filter efficiency and indoor particle concentration are the most important factors determining how fast the evaporator fouls. [Lawrence Berkeley National Laboratory / , 2002]
- A typical evaporator fouls enough to double its pressure drop in about 7.5 years, reducing airflow by 5–7% and raising fan power by 1–10%. [Lawrence Berkeley National Laboratory / , 2002]
- Replacing a dirty, clogged filter with a clean one can lower an air conditioner's energy consumption by 5–15% (US DOE). [US Department of Energy – Energy Saver, 2024]
- 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]
What we do on site
- Inspection: with plaster dust the evaporator looks uniformly white-grey, as does the roller; we photograph.
- Sealed double cover, hose to the bucket, foil on the floor (the renovation is done, we protect it).
- Alkaline solution with a longer contact time, to soften the mineral layer; adjustable pressure wash, several passes, evaporator + roller + pan + hose.
- Sanitising; filters washed; we also check the temperature sensor on the evaporator is not coated with dust.
- Outdoor unit washed in place – site dust gets there too.
- Temperature test before/after – with plaster dust the recovered split is often 4–5 °C. See current rates on the Prices page.
What you can do yourself
- Wash the filters now, twice, and replace them if they stay grey.
- Next renovation: unit off at the breaker and sealed with film and tape, not just covered.
What NOT to do
- Do not run it 'to blow the dust out' – it pushes it deeper into the evaporator.
- Do not vacuum the fins – they bend.
Prevention
After a renovation, a clean is mandatory even if the unit is new; then the normal yearly rhythm.
When to call us
0764 012 943, WhatsApp, Monday–Saturday 08:00–20:00. Băneasa is close.
Related threads
Smoking indoors – the unit has a yellow layer; how often does it need cleaning?
Explanations and useful checks for this situation: Smoking indoors – the unit has a yellow layer; how often does it need cleaning?
Restaurant: the units in the dining room have grease stuck to the fins – can they still be cleaned?
Explanations and useful checks for this situation: Restaurant: the units in the dining room have grease stuck to the fins – can they still be cleaned?
'Full dismantling' clean or in-place? One company says only dismantled is a proper clean
Explanations and useful checks for this situation: 'Full dismantling' clean or in-place? One company says only dismantled is a proper clean
15-year-old unit, never cleaned inside – worth cleaning or should I replace it?
Explanations and useful checks for this situation: 15-year-old unit, never cleaned inside – worth cleaning or should I replace it?
We bring the baby home in 2 weeks – the bedroom unit has not been sanitised for 3 years
Explanations and useful checks for this situation: We bring the baby home in 2 weeks – the bedroom unit has not been sanitised for 3 years
Multi-split with one outdoor unit and 4 indoor units — do we sanitise them all at once or one by one?
Explanations and useful checks for this situation: Multi-split with one outdoor unit and 4 indoor units — do we sanitise them all at once or one by one?
Sources (3)
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.