Aircon Smells Bad? Common Causes & Quick Solutions

Aircon Smells Bad? Common Causes & Quick Solutions

December 15, 2025

Updated for Singapore homes • Practical fixes • When to call a technician

If your aircon releases a foul or musty smell every time you turn it on, you’re not alone. In Singapore’s hot and humid climate, mould and bacteria can grow quickly inside the aircon system — especially when filters, coils, and drain pipes are not cleaned regularly.

While a mild smell may go away after basic cleaning, stronger odours often indicate deeper issues such as mould infestation, stagnant water or even a refrigerant leak. This guide covers the most common causes of aircon smells and the quickest ways to remove the odour safely.

1. Musty or Mouldy Smell

This is the most common aircon smell in Singapore homes.

A musty or “old room” smell usually means mould or fungus is growing inside the unit. Moisture trapped on the evaporator coil, blower wheel or drain pan creates the perfect environment for mould spores to spread through the air.

• Dirty or wet air filters
• Mould on evaporator coil or blower wheel
• Clogged or dirty drain pan
• High indoor humidity

How to Fix	How to Prevent
Clean or wash the air filters thoroughly.	Wash filters every 2–4 weeks.
Run the aircon on fan or dry mode to remove moisture.	Keep room humidity low with ventilation or dehumidifier.
Schedule a chemical wash to remove mould from the coil and blower.	Service your aircon every 3–6 months.

Recommendation: Book a chemical wash to remove mould and deep-clean the cooling coil.

2. Rotten or “Dead Animal” Smell

A strong rotten smell is usually caused by bacteria growing in stagnant water inside the unit. In some cases, dead insects or pests trapped inside the fan coil can also produce this odour.

• Water collected in a dirty or full drain pan
• Severe mould and bacterial growth
• Blocked or poorly sloped drain pipe
• Dead insects or small pests inside the unit

How to Fix	How to Prevent
Clean and disinfect the drain pan and clear the drainage pipe.	Make drain pan and pipe checks part of every servicing.
Use antibacterial treatment during chemical cleaning.	Run the unit on fan or dry mode occasionally to dry out moisture.
For severe odour, perform a full chemical overhaul.	Avoid long gaps (over 12 months) without deep cleaning.

Recommendation: Schedule an aircon chemical overhaul if the smell is very strong or keeps coming back.

3. Chemical or Gas Smell

A sharp chemical smell or “gas” smell can indicate a refrigerant leak from the copper pipes or cooling coil. This issue affects cooling efficiency and can be harmful if ignored.

• Leak in refrigerant piping or joints
• Corroded copper pipes
• Poor insulation or installation workmanship

How to Fix	How to Prevent
Switch off the aircon and avoid using it until inspected.	Have gas pressure checked during annual servicing.
Get a technician to test for leaks and repair faulty joints or pipes.	Ensure proper insulation and support for refrigerant piping.
Top up refrigerant only after the leak has been properly fixed.	Use experienced installers for new systems.

Recommendation: Arrange a gas leak inspection and top-up as soon as possible.

4. Burning or Electrical Smell

A burning smell, especially when paired with unusual sounds or the unit cutting off, usually points to an electrical or mechanical problem. This can be dangerous and should never be ignored.

• Overheating fan motor or compressor
• Faulty capacitor
• Loose or damaged electrical wiring

Recommendation: Turn off the aircon immediately and request an urgent aircon troubleshooting inspection.

Comparison: Which Service Do You Need for a Smelly Aircon?

Service Type	What It Includes	Best For	Odour Removal
General Servicing	Filter cleaning, basic brushing and vacuuming	Mild smell, routine maintenance	⭐ Partial improvement
Chemical Wash	Chemical cleaning of coil, blower and drain pan	Musty or mouldy smell	⭐⭐⭐ Effective
Chemical Overhaul	Full dismantling & deep sanitisation of indoor unit	Strong, persistent odour or heavy mould	⭐⭐⭐⭐ Best solution
Gas Leak Inspection	Pressure test, leak detection & gas top-up	Chemical / gas smell, poor cooling	⭐⭐ Targeted for gas-related odours

Simple Things You Can Try at Home

Before calling a technician, you can try these quick steps:

• Remove and wash the air filters, then let them dry completely before reinstalling.
• Run the aircon on fan mode for 15–20 minutes to dry up moisture.
• Open windows occasionally to ventilate the room and reduce humidity.
• Avoid spraying strong perfume, air freshener or insecticide directly into the aircon.

🛠️ When Should You Call a Technician?

Call a professional technician if:

• The smell is strong or gets worse over time.
• The odour comes back quickly after cleaning the filters.
• You notice a gas or chemical-like smell.
• There is water leaking together with the smell.
• The aircon is more than 5 years old and has never been deeply cleaned.