mitsubishi air conditionerA split system air conditioning unit circulates air inside the room. The outside unit does not mix with the air circulating through the indoor part of the unit.

If you have musty odours from your Split System, it is caused by the indoor part of the unit only, not the outdoor section.

So how do you rectify the problem?

The problem is due to either;

  • The Filters
  • The Drain Pipe

The Filters

  • Remove and clean the dust from the filters.
  • Leave to Dry
  • Replace the filters

The Drain Pipe

This is the most likely cause of the problem, due to blockage. Water is drained to the outside the building, by catching the water that is formed from condensation in a tray at the bottom of the air conditioner.

Musty Odours can occur through the following reasons;

  • If the drain pipe is completely blocked water would be overflowing inside the room
  • A partial block would cause a musty odour, while still allowing flow of water to the outside.
  • A tray that is not sitting correctly or a tilted air conditioning unit would allow the water to sit in the tray.


  • Clear the Drain Pipe
  • Make sure the air conditioner is correctly mounted and not leaning forward.

You will need to take off the Split System Inside Units Cover to rectify the problem. If you are not sure about doing this, please contact us.

The Condenser Unit

These are the fins between which the air flows.  The fins transfer heat to or from the outdoor unit depending what mode the air conditioner is in – Heat or Cool.

They could be dirty and mould may be growing between the fins.


  • Make sure there is no dust build up around fins
  • Clean around fins carefully to avoid damage to fins
  • Spray with a mould destroying compound

Contact us if you are not comfortable in carrying out these solutions or none of them fix the problem.