A musty AC smell almost always comes from mould or bacteria on the coil or in the drain pan, not the room itself. Cleaning the coil and sanitising the unit addresses the smell at its source rather than masking it.
Why the Smell Isn't Coming From the Room
If a musty smell is strongest right when the AC first switches on and fades over time, that's a strong sign it's coming from inside the unit rather than the room's furnishings or surfaces. Air fresheners and room sprays typically don't resolve it because they're not addressing the actual source.
What's Actually Causing It
A damp evaporator coil sitting in a warm, dark cabinet is close to ideal conditions for mould and bacterial growth, and that biological layer is what produces the musty odour every time air passes over it. A blocked or slow drain line, leaving standing water in the pan, makes this worse.
The Fix: Clean, Then Sanitise
A physical clean of the coil, drain pan and blower removes the visible buildup, but a musty smell that persists afterward usually means an antimicrobial sanitisation treatment is needed to actually eliminate what a rinse alone leaves behind. This combination resolves the vast majority of persistent AC odour complaints.
If this sounds like what's happening with your unit, our AC Cleaning Service page covers exactly how we handle it, or you can message us directly for a same-day assessment.
Frequently Asked Questions
Will an air freshener fix a musty AC smell?
No, it only masks the smell temporarily since it doesn't address the mould or bacteria actually producing it inside the unit.
Is a musty AC smell a health concern?
It can be, particularly for allergy or asthma sufferers, since the smell is a sign of biological growth being circulated through the air.
How quickly does the smell go away after cleaning?
Often immediately if sanitisation is included; a clean without sanitisation sometimes leaves a faint smell if biological growth was significant.