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Is Your AC Spreading Mould? What You Need to Know

Living in South East Queensland, our air conditioners are lifesavers, especially during the sweltering summer months. However, it is crucial to be aware of potential health hazards lurking within. Air conditioning systems can harbour black mould and bacteria, thriving in the dark, damp environment, which can be harmful when dispersed throughout your home, particularly as we transition our AC units to heating mode for the winter.

In this article we will explore how to know if you have mould in your AC, the importance of regular air conditioning maintenance, and tips to ensure your home stays safe and healthy year-round, whether you’re in Brisbane, the Gold Coast, the Sunshine Coast or Toowoomba.

The Perfect Environment: Why Mould Thrives In Air Conditioner Units

Air conditioners create the perfect environment for mould growth due to their moist, often dark conditions, paired with the warm, humid climate here in Brisbane and surrounding areas. Mould thrives in these settings, feeding on dust, pollen and other matter that accumulates within the indoor unit, even in the cleanest of homes.

Air conditioning with mould issues

During summer, the evaporator coil in your indoor unit cools the air and extracts moisture. This moisture drips into a drain pan and typically is removed via a condensate drain line. Although the system is designed to manage moisture, it can still linger on the indoor coil or other internal parts such as the fan barrel, louvers, or fan blades, providing the perfect breeding ground for mould.

Additionally, if the drain line becomes clogged, it slows the draining process, allowing excess moisture to build up in the drain which can also promote mould growth.

On ducted systems, leaks in the ductwork can cause condensation. Moisture within the duct can enable mould growth and spread through your ducted system.

Should I Worry? Will Mould Simply Remain Inside the Unit?

Your air conditioner can spread mould beyond the confines of the indoor system, especially in ducted systems where mould spores can circulate through the ductwork, exposing other areas of you home to potential mould growth. Additionally, airflow generated by your split, ducted or cassette system can spread mould spores throughout the home depositing them on furniture, curtains, walls and ceilings, where they can initiate new mould colonies.

As mould spores are airbourne, you could also be breathing them in unknowingly. During winter, when activating heating mode, black mould breaks down into powder, which then spreads through the air and can also initiate new mould growth. Furthermore, when this powder lands on surfaces such as benchtops, you could also be ingesting it, posing additional health risks.

Is Mould in Your Air Conditioner Dangerous?

There are many species of mould that can be found throughout your property. Stachybotrys Chartarum (Toxic Black Mould) and Penicillium, are species commonly found in air conditioners and produce allergens and mycotoxins. Prolonged exposure may lead to respiratory issues and can be a factor in cancer production*. Other symptoms of mould exposure include headaches, rashes and inflammation, coughing, dizziness and eye irritation.

Without a lab analysis it is difficult to know exactly which type of mould is lurking in your air conditioner and around your home, as mould species cannot be accurately identified just by looking at them.

Regular maintenance and keeping your AC free from mould is crucial for maintaining a healthy indoor environment. If you experience any of the above reactions and suspect mould exposure consult your healthcare professional to discuss your symptoms and appropriate treatment options.

Technician making air conditioning maintenance

How to Tell if Your Air Conditioner Has Mould?

Even if there are no visible signs of mould, mould may still be present within the system, so it is important to remain vigilant. Early indicators of mould may be a musty, earthy, or stale smell coming from your air conditioner. More obvious signs of mould in or around your unit can look like dirt or dust-like build up on the fan barrel, or black to dark green patches or spots in or around the unit.

Reduced airflow or ineffective cooling can indicate mould in your AC as mould can block air passages and coat evaporator coils, hindering the systems efficiency. Water leakage or moisture around the air conditioner can also be an indication of mould, as growth can block or slow drainage, causing the moisture to back flow and spill out of the dray tray.

Can Mould Damage Your Air Conditioner?

Mould can significantly impact the performance, efficiency, and lifespan of your air conditioner. Mould build up on the evaporator coil, air filters or within ductwork (ducted system) can restrict airflow, forcing the system to work harder, putting pressure on the system. Mould can also interfere with various components leading to malfunctions and breakdowns.

Blocked drain lines due to mould growth may also lead to frozen evaporator coils. Excess moisture within the system can cause the coils to become excessively cold and freeze over, leading to a decrease in cooling capacity and potential damage to the coil.

How Can You Protect Your AC from Mould

Eliminating mould in your air conditioner can be incredibly challenging, therefore it is essential to take all necessary steps to prevent mould from establishing itself.

Cleaning filters at the beginning of each season (every 3 months), and ensuring they are properly fitted can reduce mould’s food source (dust and other matter) and may even capture mould spores from the air.

Regularly inspecting your system and routine servicing by a qualified HVAC technician can help you catch mould early. During maintenance, an air conditioning technician dismantles the system to ensure everything is working correctly which also allows for thorough inspection of the system, including all the common places that mould likes to hide.

Can I Remove Mould Myself?

You can remove small, visual patches of mould yourself on hard surfaces of your air conditioner such as cover and louvres with a 50/50 ratio of water and vinegar allowing solution to sit for about 10 mins before wiping clean. Be sure to wear a protective mask and gloves and dispose of cleaning cloths in a Ziplock bag to prevent further contamination.

Large amounts of mould are best treated by professionals, as aggravating the mould colony can encourage spores to release into the air. Further, accessing all areas of the air conditioner where mould may be hiding can be dangerous, particularly around electrical components and challenging if unfamiliar with the anatomy of an air conditioner.

Dirty mould from air conditioning

It is important to note that mould removal products and other chemical cleaners found at supermarkets or hardware stores can cause damage to internal components by way of corrosion which can cause result costly repairs or replacement.

Mould Removal by an Air Conditioning Professional

If you suspect that you have mould in your air conditioner or if mould is identified by your technician during routine maintenance, a chemical cleaning process may be carried out.

At Ice Blast we use specialised equipment and environmentally friendly cleaning products to effectively remove mould. You can access the Safety Data Sheet for the cleaning product we use here.

Clean air conditioning without mould


Some cleaning and mould removal services may offer air conditioning mould cleaning, but not all cleaning technicians possess knowledge about the inner workings of your AC. By booking a qualified HVAC technician, you not only ensure the completion of the chemical cleaning and mould removal process, but they will also ensure that your system operates effectively. They can assess your system’s condition, providing you peace of mind and enhancing the longevity of your air conditioner.

Don’t wait until it’s too late – ensure your air conditioner is running optimally and providing a healthy home environment. Book your domestic air conditioning service today  to enjoy peace of mind and comfort all year round.