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Aircon Smells Bad? Here's How to Get Rid of the Odour
Musty, sour, or vinegar smell when the aircon kicks in? Almost always mould or bacteria growing inside the unit. Fixable.
15 - 45 minutes (DIY) or chemical wash
Difficulty: Easy to Medium Last updated: March 2026
What You Can Fix Yourself
Why Your Aircon Smells in Singapore
Singapore's year-round humidity (70-90%) creates perfect conditions for mould and bacteria to grow inside your aircon. The evaporator coil stays damp, the drain tray collects standing water, and the filter traps organic matter — all of which become breeding grounds for microorganisms.
Common smells and what they mean:
- **Musty / mouldy** — mould growth on coils or filters (most common)
- **Sour / vinegar-like** — bacteria in the drain tray or drainage pipe
- **Chemical / burning** — electrical issue or overheating component (turn off immediately)
- **Rotten egg** — dead insect or animal in the unit (more common than you'd think)
Clean Your Filters
Dirty filters trap moisture and organic particles, which breed bacteria and mould.
1. Remove filters and wash under running water with mild soap
2. Spray with diluted white vinegar (kills mould and bacteria)
3. Let dry completely in the sun before reinserting
4. If filters are discoloured or mouldy beyond cleaning, replace them
Do this every 2-3 weeks. It's the single most effective thing you can do to prevent odours.
Clean the Drain Tray and Pipe
Standing water in the drain tray becomes stagnant and smelly.
1. Turn off the aircon
2. Carefully open the unit and locate the drain tray
3. Wipe it down with a cloth dampened with vinegar solution
4. Flush the drainage pipe with vinegar and water (1:1)
If you're not comfortable opening the unit, a regular servicing ($40-$65) includes drain tray cleaning.
When to Call a Professional
Get a Chemical Wash
If filter cleaning and drain tray maintenance don't eliminate the smell, a chemical wash is the next step. This deep-cleans the evaporator coil, fan blower, and drainage system with a specialised solution that kills mould and bacteria at the source.
A chemical wash is recommended once a year in Singapore, or sooner if you notice persistent odours. Cost: $80-$130 per unit.
When It's Not Mould
**Chemical or burning smell:** Turn off your aircon immediately. This could indicate an electrical fault, overheating motor, or melting wire insulation. Do not turn it back on — call a technician.
**Rotten or dead animal smell:** Lizards and small insects occasionally enter aircon units through gaps and die inside. A technician will need to open the unit, remove the carcass, and clean the affected area.
**Gas/sweet smell:** Rare, but could indicate a refrigerant leak (some refrigerants have a slightly sweet odour). Call a professional — refrigerant is harmful if inhaled in enclosed spaces.
When to Call a Pro
If cleaning filters and the drain tray doesn't resolve the smell within 24 hours, or if you smell anything chemical, burning, or gas-like — call a professional immediately. A chemical wash usually eliminates mould-based odours completely.
Browse contractor directory →Maintenance Tip
Run your aircon on fan-only mode for 10-15 minutes after turning off cooling. This dries out the evaporator coil and drain tray, reducing mould growth.