Mold in AC: The Complete Australian Homeowner’s Guide to Spotting, Removing, and Preventing It

Mold in an air conditioner is a colony of fungal growth (most often black, grey, or dark green) that forms on the filter, evaporator coil, drain pan, drain line, blower wheel, or inside the ductwork whenever moisture sits inside the unit for too long. It happens because air conditioners pull humid Queensland air across a cold coil, and that constant cycle of condensation, warmth, and trapped organic dust creates an ideal breeding ground for mould spores. The fix is a three-part job: switch the system off at the wall isolator, physically clean every accessible surface with a mould-rated AC cleaner, and then change the conditions inside the unit (drainage, run-time, filter routine) so the mould doesn’t come back. For most Brisbane, North Lakes, Sunshine Coast, Carindale, and Moreton Bay households, a thorough filter and surface clean handles light mould, but anything growing on the coil, in the drain pan, or inside the ducting needs a professional service. The team at AC Store handles these jobs across South East Queensland with fixed-price quotes and licensed technicians.

If you’ve started catching a musty smell every time the AC kicks on, or you’ve spotted dark spots around the vents, this guide walks you through what’s actually growing in there, why it matters for your health, how to clean it properly, and how to stop it coming back.

Why Mold Grows in Air Conditioners

Air conditioners are essentially controlled dehumidifiers. Warm room air gets drawn over a cold evaporator coil, moisture condenses into liquid, and the liquid drains away through the condensate pan and drain line. The process is efficient at cooling a room, but it also means the inside of every AC unit is constantly damp, dark, and around 10 to 15 degrees Celsius. That combination is exactly what mould spores need to germinate and spread.

South East Queensland makes it worse. Brisbane sits at around 70 percent average humidity for most of the year, and the Sunshine Coast and Moreton Bay regions push higher in summer. Run a system hard from October through March, switch it off without letting the fan dry out the coil, and within a few weeks the conditions inside that indoor head are perfect for mould growth. The most common species found in residential Australian AC units are Cladosporium, Aspergillus, and (less often) Stachybotrys chartarum (black mould). All three harm indoor air quality and are especially risky for anyone with asthma, hay fever, or young children at home.

How to Tell If You Have Mold in Your AC

Mould doesn’t always announce itself with obvious black spots. A musty, damp, or earthy smell when the system starts up is the single most reliable indicator: mould releases microbial volatile organic compounds that the human nose picks up before the colony is even visible. Visible black, green, or grey spots on the filter, louvres, or vent diffusers are stage-two signs. Increased allergy or asthma symptoms when the AC is running (sneezing, congestion, wheezing, or skin irritation) strongly suggest mould spores are being blown into the living space. Water marks on the wall below an indoor unit or ceiling stains around a ducted diffuser usually mean a blocked drain line, one of the most common triggers for deeper mould growth.

If you’re noticing any combination of these signs, the next step is to physically open the unit and inspect.

What’s Legal to DIY vs What Requires a Licensed Tradesperson

Yes, mould in an air conditioner is harmful, and the risk level depends on how much is present, what species it is, and the health profile of the people in the home. For healthy adults, short-term exposure usually causes mild symptoms: a scratchy throat, runny nose, watery eyes, headaches, or sinus pressure that resolve within hours of leaving the room. For people with asthma, allergies, COPD, or any chronic respiratory condition, the same exposure can trigger acute flare-ups including coughing, chest tightness, wheezing, and shortness of breath. For immunocompromised individuals, Aspergillus exposure can lead to invasive pulmonary aspergillosis. For infants and the elderly, long-term exposure has been linked to recurring respiratory infections and new allergies developing over time.

The takeaway: any visible or smelled mould in an air conditioner should be treated as a priority. Don’t keep running the system “just for a few more days” while you sort out a clean.

How to Clean Mold From Your AC Step-by-Step

For light surface mould on the filter and visible louvres of a split system, this is a job most homeowners can handle in 45 to 60 minutes. Anything deeper (coil, drain pan, drain line, blower wheel, ductwork) is a professional job. The AC Store book a service team handles those across Brisbane and the Moreton Bay region.

Step 1: Switch the system off at the wall isolator. Use the remote to power the unit down, then switch off the dedicated AC isolator. Do not work on a live system.

Step 2: Open the front cover and remove the filter. Lift the hinged cover, slide the filter out, and place it on a towel. If you see heavy black or green growth on the filter, double-bag it and replace it rather than trying to clean it.

Step 3: Inspect the visible internal surfaces. With a torch, look at the louvres, the visible edge of the evaporator coil, and the drain channel. If the coil itself is covered in mould (rather than just the louvres and filter), stop here and book a professional service.

Step 4: Vacuum the loose surface material. Use a vacuum with a soft brush attachment on the louvres and the inside of the front cover. Do not push the vacuum onto the coil fins.

Step 5: Spray with a mould-rated AC cleaner. Use a purpose-made antibacterial spray, or a dedicated best ac mold cleaner stocked at specialist suppliers. For stubborn growth, an industrial treatment like Concrobium provides a non-toxic option that prevents regrowth. Spray onto louvres, inside the front cover, and the drain channel only. Do not soak the electrical components.

Step 6: Wipe down with a microfibre cloth. Let the cleaner sit for the recommended dwell time (usually 5 to 10 minutes), then wipe with a clean damp microfibre cloth.

Step 7: Clean or replace the filter. Rinse a standard mesh filter under cool water until clear. For pleated paper, activated carbon, or HEPA-style filters, vacuum only and replace if visibly mouldy. Air-dry the filter fully before reinstalling.

Step 8: Reassemble and run Fan-only mode. Slide the dry filter back in, close the front cover, and run the unit on Fan-only (not Cool) for 30 minutes to dry the internal surfaces. After that, run Cool for 5 minutes and confirm there’s no smell.

If the musty smell returns within 48 hours, the mould has spread deeper and a professional clean is needed. The AC Store repair team handles deep mould remediation across South East Queensland.

Where Mold Grows: A Location Comparison

Where the mould is growing changes how serious the problem is, how it should be cleaned, and how quickly it can spread.

Mold Locations, Severity, and Treatment

Location	How Common	Risk Level	DIY or Professional	Typical Treatment Cost (Pro)
Filter (mesh or pleated)	Very common	Low to moderate	DIY (clean or replace)	Included in service
Louvres and front cover	Very common	Low to moderate	DIY (wipe with mould cleaner)	Included in service
Evaporator coil fins	Common	High	Professional only	$180 to $350
Drain pan and drain line	Common	High	Professional only	$150 to $280
Blower wheel	Less common	Very high	Professional only	$250 to $450
Ductwork (ducted systems)	Less common	Very high	Professional only	$400 to $900+

A filter-only mould problem caught early is cheap and easy to fix. Once mould reaches the coil, drain pan, blower, or ducting, the cost climbs because components need full chemical treatment or replacement. Catching the problem at the filter stage saves hundreds to thousands of dollars over the life of the system.

Cleaner Comparison: What to Use on Mold

The wrong cleaner can damage the coil, corrode internal components, or void your manufacturer warranty. Here’s how the most common options compare.

AC Mold Cleaner Comparison

Product Type	Best For	Safe on Coil	Where to Buy
Purpose-made AC antibacterial spray	Routine maintenance, light mould	Yes	Aussie Pharma Direct
Simple Green air con cleaner	Filter and louvre cleaning	Yes	Bunnings (Simple Green refill)
Concrobium mould cleaner	Stubborn mould, prevents regrowth	Yes (light mist only)	Bunnings (Concrobium)
White vinegar (50/50 with water)	Filter only, very light mould	Filter only	Any supermarket
Bleach	Not recommended	No (corrosive)	Avoid for AC use
Kitchen detergent	Not recommended	No (leaves residue)	Avoid for AC use

For most homeowners doing a routine DIY clean, an AC-specific antibacterial spray paired with a cool-water rinse of the filter is the safest option. For homes with recurring mould issues across the Sunshine Coast and Moreton Bay regions, the AC Store team recommends pairing Concrobium with an annual professional coil clean. Never use bleach on or near an air conditioner: the chlorine corrodes the aluminium coil fins, damages copper refrigerant lines, and the fumes can damage the controller board.

How to Prevent Mold From Coming Back

Cleaning mould out of an AC is satisfying. Stopping it coming back is what actually saves you money and protects your family’s health long-term.

1) Run Fan-only mode for 15 to 20 minutes after every cooling session. This dries the evaporator coil, drain pan, and inside of the indoor head, removing the moisture mould needs. Modern split systems often have an Auto-clean or Dry function that does this automatically.

2) Clean the filter every 4 to 8 weeks during peak use. A clean filter blocks dust and organic material from settling on the coil. The AC Store split system quote team includes filter routine guidance with every install.

3) Check and clear the condensate drain line twice a year. A blocked drain backs water up into the drain pan and then into the unit. Pour a cup of white vinegar into the drain access point every six months to keep it flowing.

4) Set the cooling temperature to 22 to 24 degrees, not 18. Setting the system too cold makes the coil run much wetter, creating more condensation and longer drying times.

5) Book a professional service once a year. A licensed technician will deep-clean the coil, drain pan, drain line, and blower wheel, refill any preventative mould treatment, and document the service for your manufacturer warranty. The AC Store warranty team can walk you through the requirements for your brand and model.

When to Replace Your AC Instead of Cleaning It

In some cases, the mould is so widespread or the unit so old that cleaning is throwing good money after bad. Replacement makes sense when the indoor coil and ductwork both show heavy contamination, the system is 10 or more years old, the cleaning quote is more than 50 percent of the replacement cost, or the unit has had repeated mould issues despite annual servicing. A new energy-efficient split or ducted system pays back the upfront cost over 5 to 8 years through lower power bills and reduced repairs. Modern units also include better drainage design, antibacterial coil coatings, and Auto-clean drying cycles that reduce the chance of mould returning. If you’re weighing up a deep clean versus replacement, the AC Store team across the north lakes store, Kawana, and Deception Bay showrooms can quote both options.

Final Thoughts

Mould in an air conditioner is one of those problems that goes from “annoying smell” to “serious health and repair issue” much faster than most homeowners expect. South East Queensland’s humidity makes Brisbane, North Lakes, Sunshine Coast, Carindale, and Moreton Bay homes especially vulnerable, but the same conditions that make it likely also make it preventable. A 10-minute filter clean every 4 to 8 weeks, a 15-minute Fan-only run after each cooling session, and an annual professional service together prevent the vast majority of mould issues before they ever start.

If you’ve already caught a musty smell or spotted dark patches around the louvres, deal with it this week. Light surface mould is a DIY job. Anything on the coil, in the drain pan, or in the ductwork is a professional one. Either way, the AC Store crew led by Steve and James handles mould inspections, deep cleans, and full system replacements across Brisbane and the broader Moreton Bay region. Visit one of our showrooms in North Lakes, Kawana, or Deception Bay, or request a quote online and we’ll walk you through the right solution for your unit, your home, and your family’s health. Backed by responsive quote times so you know exactly what to expect before any work begins.

Frequently Asked Questions