Does Your Air-Conditioner Smell Bad?

Being an air-conditioner technician has naturally made me to become a crime scene investigator. We sometimes received calls from customer complaining that their air-conditioner smell bad. Usually the bad musty odour will last for the first few minutes when the air-conditioner is just being switch on; the smells will fade away once the compressor of the condensing unit starts running.

Before I continue to get into the details of the causes of bad odour emitting from air-conditioner, I would like to firstly clarify that air-conditioner do not produce smell at all. There is no air exchange between the indoor fan coil unit and the outdoor condensing unit. Air-conditioner cools a room by simply circulating air in the room itself, and cooling the air when the air is being circulated through the cooling coils of the indoor unit.

Over the years, we have help many of our customers identify the causes that contributes to the bad odours emitting from air-conditioner. These are some of the sources that we have identified so far.

  • Musty odours from mildew and mould form on air-conditioner (Most common)
  • Used of aromatherapy products such as essential oil/ candles
  • Used of powder and spraying of perfume near the air-conditioner indoor unit
  • Dead lizard in the air-conditioner
  • Dead rat in the trunking (Extreme Case, rarely happened, usually at landed house)

The most common sources of odours are from the accumulation of mildew and mould growing on the cooling coil/ heat exchanger and drain pan. Some air-conditioner brands have come out with auto clean function/ self clean function in-built to their remote control settings, so that users can activate the function to dry up the cooling coil/ heat exchanger after usage to prevent/ reduce mould/ mildew and bacteria from breeding which significantly reduce bad musty odours.


Not to worry. For most users whose air-conditioners do not have the in-built auto clean/ self clean function, you can simply select the MODE on the remote controller to FAN MODE before turning it off and set the FAN SPEED to HIGH. Allow the fan to run for at least 30 minutes to dry up the cooling coil/ heat exchanger before turning it off. Do not have to worry too much for electrical consumption, as the condenser do not run during fan mode operation, the electrical usage of the indoor fan motor alone is quite minimal.

Note: Please remember to set the MODE of the remote controller back COOL MODE the next time you want to use it; air-conditioner will not be cold when running on FAN MODE.

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