Burning, electrical or gas smells
For a burning smell, Mitsubishi Electric says to stop the air conditioner and disconnect the power or turn the breaker off, then call for service. If the smell near a gas heater is gas, follow Energy Safe Victoria's steps: no flames, no light switches or devices, doors and windows open, the gas off at the meter if that's safe, and a call to the emergency number on your gas bill. Remember that carbon monoxide from a faulty gas heater has no smell at all, so a heater can be dangerous even when the air smells fine.
A musty, damp or mouldy smell
Mitsubishi Electric traces it back to the filters. When they're dirty, moisture condenses inside the unit and mould gets a foothold, and the dust that collects inside can smell on its own or block the drain.
The fix starts with you and often ends there: wash the filters, air the room and dry the unit out. If the smell keeps coming back, the mould is on the coil or the fan, where you can't safely reach, and a professional clean is the answer.
Clearing a musty smell, step by step
Switch off at the power
Turn the unit off with the remote, then at the isolator or the breaker, before you touch the filters.
Wash the filters
Follow your manual. Mitsubishi Electric says to use water no hotter than 50 degrees and to dry filters thoroughly in the shade.
Air the room and dry the unit
Samsung suggests ventilating the room and running Fan mode for 3 to 4 hours. Mitsubishi Electric recommends running the fan after COOL or DRY so the inside of the unit dries out.
Watch for a few days
Use it normally. If the smell returns quickly, book a clean of the coil, fan and drain. Samsung's advice also mentions cleaning the drain, and where that means taking covers off, it's a job for the technician.
A smell that matches your house
If the aircon smells of cigarette smoke, the dog, cooking or new carpet, it may just be passing on what's already in the room. Mitsubishi Electric says a unit can suck in odours from walls, carpet, furniture and fabric and blow them out with the air.
Air the room properly and clean the filters. If the smell still clings to the unit once the room is fresh again, the inside of the unit probably needs a clean.
Smells from other heating and cooling systems
Evaporative coolers. Seeley says new Chillcel pads are slightly smelly when the cooler is first turned on, that the smell fades quickly, and that its Pad Flush function can reduce it. For smells after that, Seeley's basics are to keep the reservoir, pads and other components clean and to replace pads on the manufacturer's schedule. An evaporative cooler service covers both.
Ducted systems. A dusty or stale smell from every vent at once points away from a single unit and towards the return air filter or the ducts, which is a duct cleaning job.
Gas ducted heating. Any change in the way your heater runs deserves a gasfitter's visit. Energy Safe Victoria says that if the flame changes from its usual colour, you must get a qualified gasfitter to inspect it and check for carbon monoxide leakage.
Can you smell a refrigerant leak?
Don't count on it. Mitsubishi Electric warns that refrigerants may not have an odour. The better clue is a system that's lost its cooling or heating, which our not cooling guide works through.
What you can do, and who to call
You can
- Washing the filters the way your manual describes.
- Running Fan mode to dry the unit after cooling.
- Airing the room and looking for other sources of the smell.
- Switching off at the breaker if anything smells hot or burnt.
Leave to a licensed installer
- Cleaning the coil, fan and drain tray inside the unit.
- Tracking down a burning or electrical smell.
- Checking a gas heater for carbon monoxide, which needs a qualified gasfitter.
- Cleaning the ducts and the return air path on a ducted system.
What we'd do
Where we'd start
For a musty smell, wash the filters, run the fan for a few hours and give it a few days. If it comes back, book a proper clean of the indoor unit rather than masking it with a spray. For anything burning, electrical or gassy, switch it off first and get the right person out before it runs again: a repair specialist for the aircon, a gasfitter for the heater.
