DIY Aircon Mould Test Guide — How to Check for Mould in Your Air Conditioner

The Cassowary Coast is one of the wettest, most humid patches of Australia. That climate is brutal on split system air conditioners — every time your unit cycles off, moisture is left sitting on the coil, in the drain tray and inside the barrel fan. After a few wet seasons, most FNQ aircons quietly grow mould. This guide walks you through four DIY aircon mould tests you can do today, plus when to stop and book a professional hydro-clean.

Test 1 — The Visual Check

Turn the unit off at the wall. Open the front cover and slide the filters out. Shine a torch inside and look at the aluminium fins of the coil and the black barrel fan behind it.

• Black speckles or dots on the fan blades — mould colonies.
• Green, grey or pinkish film across the coil fins — biofilm and mould.
• White fluffy patches — a different mould strain that loves cold, wet surfaces.
• Slime or a wet film in the drain tray at the base — bacterial and mould growth.

If you can see any of the above, you don't need any further testing. Skip to the booking section.

Test 2 — The Smell Test

With the unit closed back up, set it to cool at 20°C and stand under the vents. Within 10–20 seconds a mouldy aircon will produce one of these smells:

• Wet towel or damp gym-bag smell.
• Musty basement or old book smell.
• Vinegar or sour milk hint.
• A cat-urine sharpness (this is a specific mould byproduct).

Clean split systems smell like nothing. If yours smells like anything, mould or bacteria is the most likely cause — our musty aircon guide digs deeper.

Test 3 — The White Cloth Test

Take a clean white microfibre cloth. With the unit off, reach up under the front louvres and gently wipe the visible edge of the barrel fan (the black spinning drum). Pull the cloth out and check it under natural light.

• Light grey dust only — normal, filter your unit and re-test in a month.
• Dark grey to black smears — heavy dust and beginning biofilm.
• Black flecks, greenish tint or a smell on the cloth — active mould.

Test 4 — DIY Mould Test Kits

Bunnings, Amazon AU and most hardware stores sell settle-plate or swab mould test kits for $20–$40. They work like this:

• Open the petri dish in front of the running aircon vent for the time listed on the pack (usually 60 minutes).
• Seal it and leave it somewhere dark and warm for 3–5 days.
• Compare the growth against the chart on the pack.

These kits are useful for confirming what you already suspect, or for landlords and body corporates that need a piece of paper. They don't tell you how deep the mould has gone inside the coil and drain — for that, you need a licensed tech with a hydro rig.

What a Professional Hydro-Clean Actually Removes

A full ACcleanQLD hydro-chemical clean strips every layer your DIY test can't reach: the coil face and back, the barrel fan (removed and washed separately), the drain tray, the drain line, the louvres and the filters. We treat the system with an EPA-approved anti-mould sanitiser and flush it clean. Most Cassowary Coast homes need this once a year, or every six months in salt-air areas like Mission Beach and Kurrimine Beach.

More on the health side of the story in our aircon mould health guide, or see the full cleaning service and pricing.

ARC Licensed – Lic. L194280