A bad smell from an air conditioner usually comes from dust and moisture building up in the filter, the indoor unit coil, the fan wheel and the drain tray, and from the mould and bacteria that grow there. In units left switched off for a long time, this build-up is more noticeable when they are first turned on. You can clean the filters yourself; cleaning the coil, fan and condensate drain area, however, needs professional maintenance.
Where Does the Smell Come From? Key Parts of the Indoor Unit
The smell is often strong for a few minutes when the unit is first switched on, then seems to fade. This does not mean the source has gone; your nose gets used to the smell while the build-up stays where it is. To find the source, it helps to know which parts of the indoor unit collect dirt.
Filters
The filters are the first thing the room air comes into contact with. Dust, pet hair and greasy vapour from the kitchen collect here. Combined with moisture, this dirt eventually turns into mould and a source of a heavy smell.
Coil (Evaporator)
During cooling, the surface of the coil is constantly wet. Fine dust that gets past the filter sticks to this wet surface, creating ideal conditions for micro-organisms to grow. This is the most common source of the smell usually described as "damp" or "wet socks".
Fan Wheel and Drain Tray
Mould can build up as black spots on the blades of the cylindrical fan wheel. The drain tray always holds water, so stagnant water and sediment form there. When the tray and hose become blocked, you may get both a smell and dripping water; we cover this in our article on why an air conditioner leaks water.
What Might Different Smells Indicate?
| Smell | Possible source |
|---|---|
| Mould, damp, wet socks | Moisture and micro-organisms building up on the coil, fan wheel or drain tray |
| Sewage or rotten smell | Stagnant water in the condensate drain line, or smells coming back from the point where the drain connects to a waste pipe |
| Room smells such as cigarettes or cooking | The filter and coil holding on to smells from the room |
| Dusty smell on first use | Dust that has collected in a unit not used for a long time |
| Burning or plastic smell | Could be an electrical problem |
A burning smell is different from the others; it may be a safety issue rather than a cleaning one. If this happens, switch the unit off and unplug it immediately, do not carry on using it and contact a service technician.
Smells in Units That Have Not Been Used for a Long Time
An air conditioner left off all winter, or units in holiday homes that do not run for months, can give off a noticeable smell when first switched on. Moisture left in the indoor unit during the idle period, together with accumulated dust, paves the way for mould. This is common in coastal areas with many seasonally used holiday homes, such as Didim and Kuşadası; the humidity of the sea air also speeds up the build-up.
To reduce this, you can:
- Clean and dry the filters before the end of the season.
- After using cooling, run the unit in fan mode for a while before switching it off to help the indoor unit dry out. Some models have a drying function that does this; check your user manual.
- At the start of the season, check the filters before switching the unit on and air the room when you first run it.
Cleaning You Can Do Yourself
- Switch the unit off with the remote control and unplug it.
- Lift the front cover and remove the filters.
- Wash the filters in lukewarm water; use a soft brush if needed.
- Let the filters dry completely in the shade. Fitting wet filters makes the smell worse.
- Wipe the outside of the unit and its cover with a slightly damp cloth.
- Refit the filters and switch the unit on.
During the busy summer months, checking the filters every few weeks, and more often in rooms with pets or near the kitchen, delays the smell from developing. If you see a tear or distortion in a filter, it needs replacing with a new one.
One important point: do not spray sprays, bleach or any other chemical into the body of the indoor unit, onto the coil or onto the fan wheel. These products can reach the electronic control boards, damage plastic parts and build up in the condensate drain line, causing new problems. Do not try to dismantle parts beyond the cover, remove the fan wheel or interfere with an outdoor unit mounted high up.
What Professional Maintenance Covers
Cleaning the filters can ease the smell, but if the source is in the coil, fan or condensate drain area, it will not provide a lasting fix. Professional maintenance usually includes:
- Cleaning the indoor unit coil with suitable equipment and products appropriate for the unit, while protecting the electronic parts
- Cleaning the fan wheel
- Cleaning the drain tray and hose and checking the flow
- Cleaning the filters, and replacing them if worn
- A general check of the outdoor unit and an operating check after maintenance
At Evime Servis we inspect your unit on site before maintenance and tell you what work will be done and what it will cost before we start. After maintenance the unit is switched on and checked, and the service report you sign on the phone is emailed to you as a PDF. For our maintenance services, see our private air conditioning service page, and for how often homes and workplaces need maintenance, see our air conditioning maintenance guide.
If the smell from your air conditioner persists despite cleaning the filters, you can submit a service request for your address in Didim, Söke, Kuşadası or Aydın city centre (Efeler), or contact us on +90 256 503 48 80 (WhatsApp included).
Frequently asked questions
Is the mouldy smell from an air conditioner harmful to health?
A build-up of mould and bacteria can cause discomfort, especially for people with allergies or asthma. If the smell persists, cleaning the unit is recommended.
I cleaned the filter but the smell has not gone. Why?
The smell is most likely coming from the coil, fan wheel or drain tray. Cleaning these parts requires opening the indoor unit, so it should be done as part of professional maintenance.
Is it a good idea to spray odour-eliminating spray into the air conditioner?
Spraying sprays or chemicals into the indoor unit is not recommended. Even if the smell is temporarily masked, the source remains and the product can damage electronic parts.
How often should an air conditioner be serviced?
Filters should be cleaned every few weeks during the busy months. For professional cleaning of the indoor unit, maintenance once a year, before the season, is usually sufficient.
Does running it in fan mode prevent smells?
Running the unit in fan mode for a while after cooling helps the indoor unit dry out and can reduce mould growth. However, it does not clean away existing build-up.
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Published: 25.10.2026 · Last updated: