A long block of society flats with laundry on the balconies, behind thick monsoon-green trees — After the rains the outside air is wet, and so is the inside of every unit in the block.

The musty smell when it starts up

A split AC smells musty when damp and dirt sit inside it, so clean the filter, let the unit dry out, and book a proper clean if the smell stays; a burnt smell is different, so switch off at the MCB.

From The AC in Your Flat. Updated 4 November 2026.

First, smell it properly. Damp cloth or old socks points to moisture and growth inside. Scorched plastic points to a fault, and needs a different and faster response.

Why does a split AC smell musty?

The cold coil is wet whenever the AC runs, and dust from the room sticks to it. Daikin's service page links unpleasant odours to microbial growth, writing about ducted systems, and says servicing helps clean the system. A split has no ducts, but its wet coil and tray are damp in the same way. Its troubleshooting page adds a plainer cause: the unit sometimes blows back smells it has picked up from the room. Cooking, cigarettes and pets can come back out.

Dirty filters count too. A Daikin India manual lists odour among the results of running with dirty filters, alongside poor cooling.

A long weathered block of flats with dish antennas on the roof, seen over thick undergrowth — Older blocks close to greenery stay damp for months. The unit dries out only if it is given the chance.

How do you dry the inside out?

Use the drying setting if your AC has one. Makers call it different things, and Daikin's is "mould proof operation". Daikin says it may produce a smell for a while when humidity is high. Before a long gap in use, Daikin's steps are: run that drying mode on a sunny day, turn off the plug or the dedicated breaker once it stops, and take out the remote's batteries.

If your model has no drying mode, your manual is the place to check. We found no maker advice on running the fan alone for this, so we will not give you a timing.

Does a spray fix it?

No. Daikin says not to use commercial cleaners inside. They can damage the internal parts and cause leaks. Room fresheners only cover the smell, and the coil stays as it was.

Old flats in Breach Candy with awnings and laundry on the balconies, with parked cars below — A bad smell after months switched off is common enough to plan for. Book the service before the first hot week, not during it.

What to do

Yours to do

Clean the filter with the power off and let it dry fully in the shade.
Use the drying mode if your model has one, especially after the rains.
For a burnt smell, switch off at the MCB and leave it off.

Leave to the trained person

Washing the coil, tray and blower, with the unit covered and water caught properly.
Any smell that returns soon after a clean filter and a dry-out.

Also asked

Is the smell dangerous to breathe?

We can't diagnose that, and this is not medical advice. If anyone at home has breathing trouble, switch off the AC and ask a doctor. Daikin only describes the smell as a sign the unit needs cleaning.

Should it smell of anything after a service?

It should not smell of burning. If it does, switch off at the MCB, leave it off and call the technician back.

Where this came from

Daikin Middle East and Africa, how often to service: Odours and service
Daikin, troubleshooting: Sprays, drying mode, burnt smell, long gaps
Daikin India, room AC operation manual: Dirty filters and odour, Daikin India manual

This story rests on those pages, opened or checked by 4 November 2026, and on no tests of our own. Maker pages speak for their makers, and rules and wiring differ by building, so check your own manual.