Troubleshooting

Why Does My Aircon Smell? (And What to Do About It)

Q: Why does my new aircon smell?

Brand new units can emit a plastic or chemical smell for the first few hours of use — this is normal and fades. If a 'new' aircon smells musty, it may have been stored in a humid warehouse or showroom for months. A chemical wash before regular use is recommended if the smell doesn't clear within 1–2 days.

Q: What causes a sweet smell from aircon?

A sweet or ether-like smell from your aircon usually indicates a refrigerant leak. Refrigerant (Freon or R410A) has a faintly sweet chemical odour. This is a refrigerant and electrical issue — turn off the unit and call a technician. Don't run an aircon with a refrigerant leak as it damages the compressor.

By AFIX Services · Updated April 2026 · 5 min read

Before and after aircon filter cleaning in Orchard — dirty filters are the most common cause of musty aircon smells

Different smells point to different problems. A musty smell and a burning smell are not the same issue — and the fix is completely different. Here's how to read what your aircon is telling you.

Musty or mouldy smell

Most common complaint

Smells like damp towel, mould, or an old room

Cause: Mould and mildew growing on the evaporator coil or fan blower wheel inside the unit. Singapore's humidity provides ideal conditions for mould growth — especially if the unit runs frequently, then sits idle (e.g. overnight), then runs again without the interior fully drying out.

The smell comes on immediately when you turn the unit on, sometimes fades after 10–15 minutes, then returns the next time you switch on. This is characteristic of mould on the coil or blower: the unit blows through the contaminated area on startup, then the smell disperses once the room cools.

Fix: Chemical wash. Normal servicing does not remove mould from the coil or blower — only a chemical wash that removes and treats these components will resolve the smell. If the smell returns within a week of a recent standard service, book a chemical wash rather than another standard service.

Fishy or dirty sock smell

Common in neglected units

Smells like fish, stagnant water, or drain

Cause: Bacteria growing in the drain pan or drain pipe. When the drain is partially blocked, water sits in the drain pan longer than it should and becomes a breeding ground for bacteria. The smell is particularly noticeable when the aircon first turns on and draws air across the stagnant water.

This is different from mould — the smell is more "drain-like" than musty, and the unit may also be dripping water or showing signs of leakage.

Fix: Drain flush and clean. A standard service includes clearing the drain pan and pipe, but if the bacteria have been building up for a long time, a chemical wash with full drain flush is more effective. If there's visible water dripping from the unit, read our leaking water guide first.

Burning or electrical smell

⚠ Turn off the unit

Smells like burning plastic, hot dust, or electrical

Cause: Several possibilities, ranging from harmless to serious:

Dust burn-off on first use — if the unit hasn't been used in months, dust settled on the heating elements or electrical components burns off on first startup. Typically lasts only a few minutes and doesn't return. This is normal.
Fan motor overheating — a failing or seized fan motor can overheat and emit a burning smell. Usually accompanied by unusual noise (grinding or high-pitched whine).
Electrical fault — worn wiring, a failing capacitor, or a short circuit. This is the most serious cause and can be a fire risk.

Fix: If the smell lasts more than 5 minutes on first use, or returns on subsequent use, turn the unit off at the isolator switch and call a technician. Don't continue running an aircon with an electrical smell.

Sweet or chemical smell

⚠ Refrigerant issue

Smells sweet, like ether, or faintly chemical

Cause: Refrigerant leak. R410A (the refrigerant used in most modern Singapore aircons) has a faintly sweet chemical odour when it leaks. The smell is often most noticeable near the indoor unit.

A refrigerant leak will also cause the aircon to cool less effectively over time — the unit runs but the room doesn't get cold. You may also see ice forming on the refrigerant pipes near the indoor unit.

Fix: Turn off the unit and call a technician. Running an aircon with a refrigerant leak damages the compressor over time and is not effective anyway. The leak must be located and repaired before refrigerant is topped up — just topping up without fixing the leak means it will deplete again within weeks.

Cigarette smoke or cooking smell

Environmental cause

Smells like smoke, food, or cooking oil

Cause: The aircon filter and coil absorb odours from the room over time. If someone smokes in the room, or the unit is near a kitchen, the coil and filter accumulate odour particles. When the unit runs, it recirculates these absorbed odours back into the room.

This is particularly common in rented units where previous tenants smoked, or in kitchen-adjacent bedrooms in HDB flats where cooking odours drift through.

Fix: Chemical wash to fully decontaminate the coil and blower. Regular servicing (3-monthly) to prevent re-accumulation. If the smell is persistent, run the fan mode (without cooling) for 10–15 minutes after cooking to help the unit dry out and ventilate.

Why the smell doesn't clear on its own Mould on an aircon coil is a living organism — it doesn't dry out or go away with time. As long as the unit runs in Singapore's humidity, it has the moisture it needs to survive and spread. The only way to remove it is physical cleaning with chemical solution. Running the aircon more frequently won't help.

If the smell came back after a recent service

This is the most common complaint we hear: "I just had it serviced last week and it still smells."

Standard servicing cleans what's accessible — the filter, drain pan, and exterior coil surface. It doesn't remove the fan blower wheel or deep-clean the coil. If mould has established inside the unit, a standard service won't reach it.

The fix is a chemical wash, not another standard service. A chemical wash removes the blower wheel, soaks the coil in chemical solution, and rinses all components — that's the only way to remove established mould growth.

See our full guide: Chemical wash vs normal service — what's the difference?

Persistent smell? Tell us what it's like — musty, burning, or otherwise — and we'll tell you what's causing it and what it'll cost to fix.

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Frequently asked questions

Why does my aircon smell musty even after servicing?

A standard service doesn't remove mould from the evaporator coil or fan blower. If the smell returned within a week of your last service, you need a chemical wash — not another standard service. Chemical wash removes and treats both components that normal servicing can't reach.

Is it dangerous to breathe aircon smell?

A musty aircon smell means mould spores are being blown into the room every time the unit runs. Prolonged exposure can aggravate asthma and allergies, especially in children and the elderly. It should be addressed promptly with a chemical wash.

Why does my new aircon smell?

A plastic or chemical smell from a brand-new unit is normal and fades within a few hours. If a unit smells musty and it's described as "new," it may have been stored in a humid warehouse for months — a chemical wash before regular use is recommended.

What causes a sweet smell from aircon?

A sweet or ether-like smell usually indicates a refrigerant leak. Turn off the unit and call a technician — don't continue running it. Running an aircon with a refrigerant leak damages the compressor and the cooling will worsen over time.

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