SMELLY AIRCON? WE ELIMINATE THE ODOUR AT THE SOURCE

Why Does Your Aircon Smell Bad?

You switch on your aircon expecting a blast of cool, fresh air. Instead, you are greeted by a musty, mouldy, or sour smell that fills the room. It is unpleasant, and worse than that, it could be affecting your family’s health.

At Coolbest Aircon, smelly aircon is one of the most common problems we solve. After 18+ years of servicing air conditioning units across Singapore, we can tell you this: the smell is almost always caused by biological growth inside your unit — mould, bacteria, and fungi that thrive in the dark, moist environment of your aircon’s internals.

The important thing to understand is that spraying air freshener or placing an odour absorber near your aircon does not fix the problem. The source of the smell is deep inside the unit, and the only way to eliminate it is to clean it out properly. That is exactly what we do.

Types of Aircon Smells and What They Mean

Not all aircon smells are the same. The type of odour can tell us a lot about what is happening inside your unit:

Musty or Mouldy Smell

The most common aircon odour. This damp, earthy smell is caused by mould and mildew colonies growing on the evaporator coil, blower fan, and drainage tray. Singapore’s tropical humidity — combined with the constant moisture inside your aircon — creates a perfect breeding ground for mould.

You may notice this smell is worse when the aircon first starts up, as the initial burst of air pushes out concentrated spores. It may lessen after running for a few minutes but never completely goes away.

Sour or Vinegar Smell

A sharp, acidic smell usually points to bacterial growth in the drainage system. When condensation water sits in the drainage tray for extended periods — especially in units that are used intermittently — bacteria break down organic matter in the water, producing acids that create that vinegary odour.

Stale or Stuffy Smell

This is a milder version of the musty smell. It often occurs in units that have not been serviced in a while but are not yet severely contaminated. The smell is caused by a thin biofilm of dust and biological matter on the coil and fan. While not as alarming as a strong mouldy smell, it still indicates that cleaning is overdue.

Chemical or Plastic Smell

A chemical smell from a new aircon is normal — it is the outgassing of new plastic components and typically fades within a few days. However, a chemical smell from an older unit could indicate overheating wiring, a failing motor, or melting insulation. This should be investigated promptly.

Rotten Egg or Sulphuric Smell

This is the least common but most alarming. It can be caused by a dead lizard or insect that has entered and died inside the unit — not unusual in Singapore where geckos are everywhere. In rare cases, it could indicate a gas leak (though most modern refrigerants are odourless).

Sweet or Fruity Smell

An unusual sweet smell can sometimes indicate a refrigerant leak, particularly with older R22 refrigerant. If you notice a sweet, chemical-like odour combined with poor cooling, have the system checked for a gas leak promptly.

Where Does the Smell Come From?

The smell originates from specific components inside your aircon:

Evaporator Coil

The coil’s tightly packed aluminium fins provide an enormous surface area — ideal for mould to colonise. When warm, humid air passes over the cold coil, condensation forms on every surface, creating the moist environment mould needs. Dust particles in the air stick to the wet surface, providing nutrients for biological growth.

Blower Fan (Barrel Fan)

The blower fan sits directly behind the evaporator coil and is exposed to the same damp conditions. Its cylindrical shape with dozens of blades creates countless hidden surfaces where mould and bacteria accumulate. Because the fan is enclosed within the unit, it never dries out completely.

Drainage Tray

Sitting beneath the evaporator coil, the drainage tray collects all the condensation. If it does not drain quickly enough — or if the drain pipe is partially clogged — water sits and stagnates, becoming a breeding ground for bacteria and algae. This is often the source of sour or vinegary smells.

Air Filters

While filters are the easiest component to clean, they can also harbour mould if they stay damp. In severe cases, mould growth on filters is visible as dark spots.

Health Risks of a Smelly Aircon

A smelly aircon is not just an inconvenience — it is a health concern. The same mould and bacteria causing the odour are releasing airborne spores and toxins into the air your family breathes. Here is what that can lead to:

• Allergic reactions — Sneezing, runny nose, itchy eyes, and skin irritation. Mould spores are a common allergen that affects many Singaporeans.
• Asthma aggravation — For family members with asthma, airborne mould spores can trigger attacks. Studies show that indoor mould exposure is a significant asthma trigger.
• Respiratory infections — Certain bacteria that thrive in aircon units can cause respiratory infections, particularly in young children, elderly family members, and those with compromised immune systems.
• Headaches and fatigue — Prolonged exposure to mould-contaminated air can cause persistent headaches, fatigue, and difficulty concentrating.
• Sick Building Syndrome — In offices, contaminated air conditioning is a leading cause of sick building syndrome, where occupants experience health symptoms that improve when they leave the building.

This is why we take smelly aircon seriously. It is not just about comfort — it is about your family’s health.

How We Eliminate Aircon Odours

Option 1: Chemical Wash (For Moderate Smell)

If the smell started recently or is mild to moderate, a chemical wash is usually sufficient. Our chemical wash involves:

1. Spraying specialised cleaning solution onto the evaporator coil and blower fan
2. Flushing the drainage system to remove bacterial buildup
3. Rinsing all components with pressurised water
4. Applying anti-bacterial and anti-fungal treatment

A chemical wash effectively removes surface-level and moderate mould contamination, restoring fresh airflow.

Option 2: Chemical Overhaul (For Severe or Persistent Smell)

For units with heavy mould growth, long-standing odour issues, or cases where a previous chemical wash did not fully resolve the smell, a chemical overhaul is the answer:

1. Complete disassembly of the indoor unit
2. Individual soaking of evaporator coil, blower fan, and drainage tray in concentrated chemical solution for 20 to 30 minutes
3. Hand scrubbing of all components
4. High-pressure rinsing
5. Anti-bacterial and anti-fungal coating
6. Reassembly and testing

The chemical overhaul reaches contamination that a chemical wash simply cannot. By soaking each component individually, we ensure 100% of the mould and bacteria is eliminated.

Our Recommendation

Start with a chemical wash — it resolves the odour in 80% of cases. If the smell is persistent, severe, or the unit has not been serviced in over a year, go directly for a chemical overhaul to save time and money on a potential second visit.

Pricing for Smelly Aircon Treatment

Service	Price	Best For
Chemical wash	From S$80/unit	Mild to moderate smell
Chemical overhaul	From S$120/unit	Severe or persistent smell
Anti-bacterial treatment (standalone)	From S$30/unit	Preventive maintenance

We bundle the anti-bacterial treatment with every chemical wash and overhaul at no extra charge. For customers who want standalone anti-bacterial treatment between deep cleans, we offer it as a separate service.

Preventing Aircon Smells From Coming Back

After we have eliminated the odour, here is how to keep it from returning:

Run Fan Mode Before Shutting Off

This is the single most effective prevention tip. After you finish using the aircon, switch to fan mode for 30 minutes before turning it off completely. The fan circulates air through the unit without cooling, drying out the evaporator coil and drainage tray. Dry surfaces do not grow mould.

Many modern Daikin and Mitsubishi Electric units have an auto-dry function that does this automatically. Check your remote for an “Internal Clean” or “Dry” mode and enable it.

Clean Filters Fortnightly

Dirty filters trap moisture and organic matter, creating a food source for mould right at the front of your unit. A quick rinse every two weeks prevents this buildup.

Schedule Regular Chemical Washes

A chemical wash every 6 months prevents biological contamination from reaching the levels that cause noticeable odour. Think of it as preventive medicine for your aircon.

Ensure Proper Drainage

A slow-draining condensate pipe allows water to sit and stagnate, feeding bacterial growth. If you notice your aircon dripping water or taking a long time to stop dripping after shutting off, the drainage may need attention.

Ventilate the Room

Opening windows occasionally allows fresh air to circulate and reduces the humidity load on your aircon. Even 15 to 20 minutes of ventilation on a less humid day makes a difference.

Do Not Ignore a Smelly Aircon

A bad smell from your aircon is more than a nuisance. It is a sign that your unit is contaminated with biological growth that is being blown into your living space with every breath. The longer you wait, the worse the contamination gets, the harder it becomes to clean, and the greater the impact on your family’s health.

Contact Coolbest Aircon at 9182 5233 or email hello@coolbestaircon.com to schedule your odour elimination service. We offer same-day appointments across Singapore, and every service comes with anti-bacterial treatment and our 90-day workmanship warranty.

If you are also experiencing poor cooling, water dripping, or unusual noises, mention these when you call — they often share the same root cause as the smell, and addressing everything together is more efficient and cost-effective.