Some signs are hard to miss. Others get blamed on the weather, the family cat, or the kids leaving the door open. Here are the real ones.
1. Musty smell
Especially in the first 60 seconds after the unit turns on. That's biofilm on the coil being warmed and aerosolised.
2. Black spots on vent louvres
Mould. If it's visible on the outside, there's a lot more you can't see inside.
3. Water dripping from the front
The drain line is partially blocked with sludge or the drip tray is overflowing because of biofilm.
4. Reduced airflow
Filter and coil both restrict air when caked.
5. Higher power bills
See the article on dirty units and running costs.
6. Louder than usual
An out-of-balance barrel fan caked with grime rattles.
7. Sinus or allergy flare-ups
Especially in the room the unit is in.
8. Longer to cool the room
Compressor working harder against a fouled coil.
9. Ice on the coil
Restricted airflow drops coil temperature below freezing. A serious warning sign.
10. It's been over 12 months
If you can't remember the last clean, it's due.
