Mould in Your Air Conditioner: Health Risks & How to Fix It
- Apr 16, 2026
- Troubleshooting
If you have noticed a musty smell coming from your air conditioner, there is a good chance mould is growing inside the unit. In Brisbane’s warm, humid climate, air conditioning systems create the perfect environment for mould — dark, damp, and constantly cycling moisture. Left untreated, mould in your AC can affect your health, reduce system efficiency, and spread throughout your home.
Why Mould Grows in Air Conditioners
Your air conditioner removes moisture from the air as it cools. This condensation collects on the evaporator coils, drips into the drain pan, and flows out through the drain line. When any part of this system stays damp — which it almost always does in Brisbane — mould spores have everything they need to thrive: moisture, warmth, and organic matter (dust and debris that accumulates on coils and filters).
Common locations for mould growth include:
- Evaporator coils — constantly damp from condensation
- Drain pan — standing water if the drain is slow
- Filters — trapped dust and moisture create a breeding ground
- Air ducts — in ducted systems, ducts in roof spaces can accumulate condensation
- Blower fan and housing — hidden mould behind the unit’s front panel
Health Risks of Mould in Your Air Conditioner
When your AC runs, it blows air across mould-contaminated surfaces and distributes mould spores throughout every room connected to the system. This can cause or worsen a range of health issues:
Respiratory Problems
Mould spores irritate the airways and can trigger coughing, wheezing, shortness of breath, and chest tightness. People with existing respiratory conditions like asthma or chronic bronchitis are particularly vulnerable. Studies have shown that exposure to indoor mould increases asthma severity and frequency of attacks.
Allergic Reactions
Mould is one of the most common indoor allergens. Symptoms include sneezing, runny or blocked nose, itchy eyes, and skin rashes. If your allergy symptoms improve when you leave the house and return when you come home, your air conditioner could be the source.
Sinus Infections
Chronic exposure to mould spores can lead to fungal sinusitis — a persistent sinus infection that does not respond to standard antibiotics. This is more common than many people realise, particularly in humid climates like Brisbane.
Who Is Most at Risk?
- Children and infants (developing immune systems)
- Elderly people
- People with asthma, allergies, or compromised immune systems
- Anyone spending extended time indoors with the AC running
Signs Your Air Conditioner Has Mould
- Musty or earthy smell when the AC runs — the most common indicator
- Visible black, green, or grey spots on vents, filters, or around the indoor unit
- Allergy symptoms that worsen indoors — sneezing, coughing, itchy eyes when the AC is on
- Damp or stale air despite the system running normally
- Black residue around air vents — mould spores being distributed through the ductwork
How to Get Rid of Mould in Your Air Conditioner
What You Can Do
- Clean or replace filters: Remove filters and wash with warm water and mild detergent. Let them dry completely before reinstalling. If filters are heavily contaminated, replace them.
- Wipe visible mould on vents: Use a damp cloth with a mild mould-killing solution. Do not use bleach near electrical components.
- Run fan-only mode after cooling: Running your AC in fan mode for 10-15 minutes after cooling helps dry out the coils and reduces moisture buildup.
What Requires a Professional
Surface cleaning only addresses what you can see. The worst mould growth is typically on the evaporator coils, blower fan, and inside the drain pan — all of which are hidden behind panels and require disassembly to access. A professional AC cleaning service includes:
- Complete disassembly of the indoor unit
- Deep cleaning of evaporator coils with antimicrobial solution
- Cleaning of blower fan, drain pan, and housing
- Drain line flush to remove blockages
- Antimicrobial treatment to prevent regrowth
- Filter replacement if needed
For ducted systems, professional duct cleaning may also be necessary if mould has spread into the ductwork.
How to Prevent Mould in Your Air Conditioner
- Service annually: Regular professional servicing catches mould early and keeps coils clean.
- Clean filters monthly: Especially during Brisbane’s humid summer months.
- Run fan mode after cooling: 10-15 minutes of fan-only operation dries the coils and starves mould of moisture.
- Keep the drain line clear: Pour a cup of white vinegar down the drain every 3 months to prevent algae and mould buildup.
- Maintain indoor humidity below 60%: Use the dehumidification mode on your AC if your home feels humid even when cool.
- Ensure adequate ventilation: Especially in bathrooms, laundries, and kitchens — these rooms add moisture that your AC then has to handle.
Brisbane Climate and Mould: Why It Matters Here
Brisbane averages 60-75% relative humidity during summer. This means your air conditioner is working overtime to extract moisture, creating ideal conditions for mould growth inside the unit. In southern Australian cities with drier climates, AC mould is less of an issue. In Brisbane, it is almost inevitable without regular maintenance.
Concerned About Mould in Your AC?
Sun City Air provides professional air conditioning cleaning and mould treatment across Brisbane, Moreton Bay, and the Redcliffe Peninsula. If your AC smells musty or you are experiencing unexplained allergy symptoms, we can inspect your system and provide a thorough clean.
Call us on 07 3283 5566 or request a quote online.
