Aircon Not Cold? 7 Real Causes — and What to Check First

Few things are more frustrating than an aircon that's clearly switched on but isn't cooling. The set temperature is at minimum, the fan is blowing, and the room still feels warm. Before assuming the unit needs replacing — it almost never does — work through the causes below. Several are things you can check in minutes.

Check these first (free, two minutes)

• Mode and temperature. Make sure it's on “Cool”, not “Fan” or “Dry”, and that the set temperature is below room temperature. It sounds obvious, but a bumped remote is a surprisingly common culprit.
• The filter. Slide it out and look. If it's grey with dust, that alone can cripple cooling. Rinse, dry, refit.
• The outdoor unit. Walk outside and check the compressor isn't smothered by leaves, rubbish or a blocked wall. It needs clear airflow to dump heat. Also confirm it's actually running.

The seven real causes

• 1. A clogged filter. The most common and most preventable. Blocks airflow, so cool air barely reaches the room.
• 2. Fouled coils. A film of dust and mould on the evaporator coil insulates it, so it can't absorb heat. The unit runs constantly but never gets the room properly cold. This needs a chemical wash.
• 3. Low refrigerant. If gas has leaked, the system loses cooling power. The fix is finding and repairing the leak, then recharging — not a blind top-up.
• 4. A dirty or blocked outdoor unit. If the compressor can't release heat outside, the whole system struggles, no matter how clean the indoor unit is.
• 5. A unit too small for the room. A 1.0HP unit in a large, sunny living room will run flat out and never win. Sizing matters.
• 6. Wrong copper pipe or poor installation. Undersized or badly fitted piping starves the system. Common on rushed installs.
• 7. A failing compressor or capacitor. The compressor is the heart of the system. If it's faulty, the unit blows air but produces no cold. This is a repair, not a clean.

“It's still not cold even after a service”

This is one of the most common complaints we hear — and usually it means the service didn't actually do what it should have. A quick filter-wipe leaves the coil and blower untouched, so the real cause is still there. If your unit was “serviced” recently and still isn't cooling, the problem is likely what was skipped. A proper clean reaches the coil and blower; read what a real chemical wash looks like so you know what you're paying for.