Guide · Air conditioner
Smelly air conditioner: causes and fixes
Almost always the smell comes from dirty filters, mould on the indoor coil or standing water in the condensate tray. Cut the power, wash the filters and then let the split dry with ventilation only. If you smell burning, switch off immediately, turn off the air conditioner's breaker in the fuse box and do not switch it back on.
30 minutes Difficulty: EasyUpdated 25 October 2026
Cut the power before opening the panel. If you smell burning or plastic, or see smoke, switch off the air conditioner's breaker and do not switch it back on. The air conditioner's refrigerant has no smell: if you smell gas, open the windows, do not touch switches, shut off the gas meter, go outside and call the gas emergency service or 112.
What you need
- Vacuum cleaner
- Bowl with lukewarm water and neutral detergent
- Soft cloth
- Torch
Step by step
Tap a step to mark it as done.
What the smell tells you
Damp, cellar or stuffy: this is the most common case. The split works with damp air on cold, wet surfaces, and when it sits switched off and closed, mould grows on the coil and fan. It happens above all at the start of the season, after months of not being used.
Sour smell, like vinegar: it usually has the same origin, dust and moisture left for a long time on the coil and condensate tray. If it stays even after washing the filters, those parts must be cleaned thoroughly by the engineer.
Sewage: almost always the condensate pipe ends in a household drain without a trap, or with a dry trap. The trap is the bend that holds a little water and blocks smells. Without it, sewer air comes up the pipe and the split blows it into the room. It is solved by fixing the drain. Air fresheners do not help.
Smell of burning, gas, or when first switched on
Smell of burning, plastic or electrics: the manuals ask you to stop the appliance and cut the power, because carrying on using it can cause faults, electric shocks or fires. Do not switch it back on to see if it happens again.
If the smell comes only in the first minutes after switching on and then disappears, it is usually smells absorbed from the room or moisture left inside from the last time. Clean the filters and get into the habit of leaving a few minutes of ventilation before switching off.
The refrigerant gas inside the split has no smell, as the Daikin manual points out, for example. If you smell gas at home, the source is almost certainly your home's gas system: follow the safety rules at the top of this page.
Sprays, vinegar and sanitising
Sanitising sprays leave a scent for a few days, but they do not reach the fan and do not remove the film from the tray. Use them only if the manual allows and only on parts you can see.
Avoid spraying vinegar, alcohol, bleach or home-made mixes into the split: they damage plastic and fins, and splashes on the electrics can cause faults. For the same reason, no water jets inside the unit.
When the smell comes back even with clean filters, you need sanitising. The internal parts are taken apart, and the coil, fan, tray and drain are washed with specific products and the operation is tested. For a home split the recommended frequency is once a year, before summer.
When to stop and call a technician
- Smell of burning, plastic or smoke from the split: cut the power and do not switch it back on
- Damp smell that returns even after washing the filters
- Visible mould on the fan or on the fins behind the filters
- Sewage smell coming from the split or from the hole where the pipes pass
- The smell comes together with water drops indoors or a flashing light
Frequently asked questions
Why does the air conditioner smell damp?
Moisture and dust stay inside the split, and mould grows on the coil and fan. Wash the filters and dry the split with ventilation. If the smell stays, a sanitising service is needed, which you can ask us for in Campania.
Why does the air conditioner smell when first switched on?
In the first minutes the split pushes out the air that has been standing inside, with smells absorbed from the room and moisture from the last use. If it goes away quickly, cleaning the filters is enough. If it lasts, there is dirt to remove.
The air conditioner smells of vinegar. Is that dangerous?
It usually means dirt and moisture left inside the unit for a long time. There is no need to rush, but it should be cleaned thoroughly, especially if anyone at home has allergies.
Why does the air conditioner smell of sewage?
Almost always because the condensate pipe drains into the home's sewer without a trap, or with a dry trap. Smells come up the pipe and the split pushes them into the room: the drain has to be fixed.
The air conditioner smells of burning. What do I do?
Switch it off, cut the power at the fuse box and do not switch it back on. It may be an electrical component overheating, and an engineer must check it before it is used again.
The air conditioner smells of gas. Is it the refrigerant?
Very unlikely, because refrigerant gas has no smell. Treat it as a possible leak in the home's gas system: windows open, no switches, meter closed, out of the house and a call to the gas emergency service or 112.
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