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Aircon Troubleshooting · Singapore

Why Does My Aircon Smell Bad?

A musty or sour smell is mould and bacteria on the coil and drainage tray. A chemical wash clears it at the source. (A burning smell is different — and urgent.)

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The short answer

A musty / sour smell = mould and bacteria on the wet evaporator coil and drainage tray, blown into your room. A chemical wash dissolves and flushes it out. A burning / electrical smell is a different, urgent problem — switch off and get it checked.

What the smell tells you

Match the smell to the cause and the fix.

Mould and bacteria on the coil

The damp, sour, “dirty socks” smell. Mould and bacteria thrive on the constantly-wet evaporator coil and get blown into the room. This is the cause in the large majority of cases.

Chemical wash from $110

Stagnant water in the drainage tray

A clogged or slow drain leaves standing water that turns foul and breeds bacteria. Clearing and cleaning the drainage path removes the source.

Chemical wash from $110

Severe, long-neglected buildup

If the unit hasn’t been deep-cleaned in years and a wash doesn’t fully clear the smell, the buildup is too deep for in-place cleaning — every component needs to be removed and cleaned individually.

Chemical overhaul from $150

Burning / electrical smell (different problem)

A burning or hot-plastic smell is NOT mould — it’s electrical, and it’s urgent. Turn the unit off at the wall and get it checked before running it again.

Aircon repair from $50

What you can try first

Safe to do before booking a clean.

  • 1Run the aircon on “Fan” mode for 10–15 minutes to dry the coil — this can reduce a mild musty smell temporarily.
  • 2Remove and wash the filter; a dirty filter holds odour.
  • 3Check the drainage outlet outside isn’t blocked with stagnant water.
  • 4If the smell is burning or electrical (not musty), switch off at the wall immediately and don’t run it.

When to call a technician

Fan-mode drying and a filter wash only mask a musty smell — the mould is on the coil and inside the drainage tray, which needs chemical cleaning to actually remove. And any burning or electrical smell should be checked before you run the unit again.

We deep-clean the coil and drainage, clear the source of the odour, and have your aircon smelling fresh again — usually same day. Chemical wash across Singapore from $110.

Other aircon problems

Aircon not coldAircon leaking waterAircon noisy

Aircon smells bad — FAQs

Why does my aircon smell musty or sour?
A damp, musty smell is the classic sign of mould and bacteria growing on the evaporator coil and in the drainage tray. Singapore’s humidity keeps the inside of the unit wet, and without a deep clean, mould colonises it and gets blown into your room every time the aircon runs.
Will a chemical wash get rid of the smell?
Usually yes. A chemical wash uses cleaning solutions to dissolve and flush out the mould and bacteria that cause the odour — the source filter-level servicing can’t reach. If the unit is severely neglected and the smell persists, a chemical overhaul (full disassembly clean) is the next step.
My aircon smells like burning — is that the same thing?
No — a burning or electrical smell is different and more urgent. It points to an electrical fault (wiring, motor, or capacitor), not mould. Turn the aircon off at the wall and book a repair; do not keep running it, as electrical faults can be a fire risk.
How do I stop the smell coming back?
Keep up regular servicing every 3–4 months, and run the aircon on “Fan” mode for a few minutes before switching off so the coil dries out instead of staying damp. A deep chemical wash every 1–2 years keeps mould from re-establishing.

Get the smell gone for good.

Same-day chemical wash across Singapore. Transparent pricing — you know the cost before we start.

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