Why air conditioners grow mould on the coil and drain — and how servicing split and ducted systems across Melbourne clears it and the musty smell.
8 min read FreshDuct Melbourne Melbourne, Victoria
That musty smell when the air conditioner kicks in is usually mould. An AC’s cooling coil makes condensation by design, and if the coil, drain pan and condensate line stay damp and dirty, mould grows there and gets blown into the room with the air. FreshDuct services split and ducted air conditioning across Melbourne — cleaning the coil, pan and drain and keeping the unit clean and draining — to clear the mould and the damp, dirty conditions that cause it.
Musty SmellThe classic sign of mould in the unit
Coil & DrainWhere damp + dust grows mould
Service FixClean & draining so it dries out
An air conditioner’s cooling coil produces condensation by design, draining away through a condensate line. If the coil, drain pan and line stay damp and dirty, mould grows there and the smell and spores are blown into the room. Servicing keeps the coil, pan and drain clean and clear.
Why Air Conditioners Grow Mould
An air conditioner is, in effect, a moisture-making machine — its cooling coil condenses water out of the air as it cools and dehumidifies. That’s normal and intended. The trouble starts when the unit isn’t kept clean: dust drawn through the filters settles on the damp coil and in the drain pan, and that combination of moisture and organic material is exactly what mould needs. So an air conditioner that’s damp by design and dirty by neglect becomes a place mould readily grows — and then distributes into the room with every cycle.
The Coil, Drain and Damp
The key components are the cooling coil, the drain pan beneath it, and the condensate line that carries the water away (see the diagram above). In a clean, well-draining unit, the condensation drains off and the unit dries between cycles. In a neglected unit, the coil and pan stay damp, dust and grime accumulate, the drain may partially block, and mould establishes on those damp, dirty surfaces. Keeping the coil, pan and line clean and clear — so the unit drains and dries — is what prevents mould taking hold.
Signs of Mould in Your AC
The clearest sign is a musty smell when the air conditioner runs, especially on start-up. You may also see mould or grime around the vents, on the visible parts of the indoor unit, or on the filters, and notice allergy or respiratory symptoms when the unit’s running. A musty-smelling air conditioner shouldn’t be ignored — it’s blowing that smell, and spores, into the room. If you notice these signs, the unit needs cleaning and servicing.
Servicing Stops It
Servicing is both the cure and the prevention. A service cleans the coil and filters, clears the drain pan and condensate line, and removes the mould and the dust and grime feeding it — so the unit runs clean and dries properly between cycles. For a neglected, heavily affected unit, a thorough clean restores it; keeping it serviced then stops the mould returning. This is routine air conditioning maintenance that also happens to be the answer to AC mould. See our split system service library.
Ducted and Split Systems
Both split systems and ducted air conditioning can grow mould, and both are addressed by keeping the units clean and draining. Ducted systems add the ductwork into the picture — if the air conditioning is harbouring mould, the connected ducts are worth checking too, since the two share the same air. We service split and ducted systems and, where relevant, address the ducts as well, so the whole air-conditioning system is clean and dry. See our mould in air ducts guide.
Getting a Quote
Cleaning mould from air conditioning is quoted per job after assessing the system — the type and number of units, how affected they are, and access all matter. We assess, recommend the right service, and provide a clear quote. Call 0431 918 137 or request an inspection. See our cost & quoting guide.
Frequently Asked Questions
Why does my air conditioner smell musty?
A musty smell from an air conditioner is a classic sign of mould inside the unit. The cooling coil produces condensation by design, and if the coil, drain pan and condensate line stay damp and accumulate dust and grime, mould grows there — and the smell (and spores) get blown into the room when the unit runs. The fix is to clean the coil, pan and drain and keep the unit clean and draining so it dries between cycles. See the diagram above and our split system library.
How does mould grow inside an air conditioner?
By design, an air conditioner’s cooling coil condenses moisture out of the air — that’s how it dehumidifies — and that condensation drains away through a pan and condensate line. The problem comes when the coil, pan and line stay damp and collect dust and grime: that damp, dirty environment is ideal for mould. Combined with the dust drawn through the filters, the unit becomes a place mould establishes and then distributes into the room. Regular servicing keeps it clean and draining, which prevents this.
Can mould in air conditioning be cleaned out?
Yes — servicing the air conditioner addresses it: cleaning the coil and filters, clearing the drain pan and condensate line, and removing the mould and the dust and grime it grows on, so the unit runs clean and dries properly between cycles. For a unit that’s been neglected and is heavily affected, a thorough clean restores it. Keeping it serviced then prevents recurrence. We service split and ducted air conditioning and address the mould and the conditions causing it. See our mould in air ducts guide.
Is it bad to run an air conditioner with mould in it?
Running an air conditioner that has mould inside means it can blow spores and a musty smell into the room whenever it operates, affecting the air you breathe — and people with asthma, allergies or sensitivities may be more affected. It also means the problem continues and worsens. The sensible response to a musty-smelling or visibly mouldy unit is to have it cleaned and serviced rather than keep running it. See our black mould & health guide.
How much does it cost to clean mould from air conditioning?
It’s quoted per job after assessing the system, because the scope depends on the type of unit (split or ducted), how many units, how affected they are, and access. A single split system and a ducted system or multiple units are different jobs. We assess, recommend the right service, and provide a clear quote. Like any trade, a minimum call-out applies. Call 0431 918 137 or request an inspection. See our cost guide.
Mould or Damp Problem? Request an Inspection
We find the moisture cause, remediate the mould, and stop it coming back — across Melbourne. Call or request a quote.
