When you turn on the air con you notice a slight musty smell as the unit kicks in, perhaps unexplained sneezing or simply air that just doesn’t feel quite right. These can all point to one thing, which is mould growing from within the system.
It’s more common than people expect, and because your air conditioner circulates air throughout your home, the effects aren’t confined to the unit itself. Mould spores can travel from room to room every time the system runs. Of course, getting on top of it early (and even understanding what causes it) can make a real difference.
Why Mould Develops Inside Air Conditioning Systems
Moisture is at the core of the problem. Because as part of the cooling process, warm air passes over cold evaporator coils, causing condensation to form. Most of this drains away, but small amounts can linger and particularly in systems that aren’t cleaned or serviced regularly. Add dust and debris into the mix, and you’ve got a surface where mould can quietly take hold.
The internal environment of an air conditioner also works in mould’s favour as there’s limited light, restricted airflow in certain components, and particles that accumulate in filters and ducts all create conditions where spores can multiply without any obvious signs.
High indoor humidity compounds the issue so when moisture levels in the home are consistently elevated, the air conditioner works harder to manage them and therefore residual condensation builds up more quickly. Without routine attention, this can escalate from a minor buildup to a problem that spreads well beyond the unit.
Signs There May Be Mould in Your Air Conditioner
A musty or stale smell when the system is running is usually the first indicator. It tends to get stronger the longer the unit is on, and even a mild odour is worth investigating as it often signals early stage growth that’s easier to deal with before it spreads.
Visible signs can appear over time too and may include dark spots or patches on the filters, vents, or accessible internal surfaces are common. These can look like ordinary dirt at first, but if they return quickly after cleaning, mould is likely the cause.
Pay attention to how you feel when the system is running as increased sneezing, coughing, headaches, or irritation that eases when you step outside can indicate airborne spores circulating through the home.
How to Remove Mould Safely and Effectively
For minor, surface level cases, cleaning the accessible parts of the unit is a reasonable first step. Switch the system off, remove and clean the filters, and wipe down surfaces with an appropriate cleaning solution. Crucially, allow everything to dry completely before reassembling as residual moisture left behind can restart the cycle.
The challenge is that mould doesn’t always stay where it’s easy to reach. It can develop deeper within the system where standard DIY cleaning won’t fully address it. In these cases, having a professional air con specialists to service the unit and treat the affected areas properly.
There’s also a safety consideration worth keeping in mind as disturbing mould can release additional spores into the air, particularly in enclosed spaces. Approaching the process carefully (or calling in a professional) will ensure the problem is resolved thoroughly rather than just temporarily managed.
Some Ways to Prevent Mould From Returning
Prevention largely comes down to routine. Regularly cleaning or replacing filters keeps dust and debris from accumulating, which reduces the chance of moisture settling in hidden areas of the system.
Running the unit in fan mode periodically especially after cooling cycles helps dry out any residual moisture inside the system. Keeping indoor humidity in check, particularly during the warmer months, also goes a long way.
Beyond what you can do yourself, professional air con servicing is the most reliable safeguard. A thorough service checks internal components, addresses early warning signs before they develop, and keeps the system running efficiently.
Keeping Your Air Clean and Your System in Good Shape
Mould in an air conditioner tends to develop gradually, which is part of what makes it easy to overlook. Staying alert to the signs and keeping up with basic maintenance are the most practical ways to stay ahead of it. And when the issue goes beyond surface cleaning, or keeps coming back despite your efforts, it’s a strong signal that the system needs a proper assessment.