Aircon Not Cooling? Seven Causes, Ranked

"It's blowing, but it's not cold." It is the most common call we get, and the causes range from a filter you can wash yourself to a compressor replacement. Here they are in rough order of how often we find each one.

1. Blocked filters

Cost to fix: nothing. Restricted airflow across the evaporator means less heat is picked up from the room, so less is rejected outside. The unit runs continuously and never quite gets there.

Pull the filters out, wash them in warm water, let them dry completely, put them back. In a windy coastal city this needs doing far more often than the manual suggests. A genuine share of our call-outs end here, and we would rather you tried it first.

2. A fouled outdoor condenser

Cost to fix: a service. The outdoor coil has to dump the heat somewhere. Caked in salt, dust and grass seed, it cannot. Head pressure climbs, efficiency falls, and cooling capacity drops noticeably.

Look at your outdoor unit. If you cannot see clean metal between the fins, that is your answer. See our guide on coastal corrosion for why this is so much worse here than inland.

3. Refrigerant loss through a leak

Cost to fix: moderate, if done properly. This is the one the industry handles badly. A sealed refrigeration circuit does not consume refrigerant. If the charge is low, it has leaked - typically at a flare joint, a braze, or through a corroded section of outdoor coil.

Topping it up without finding the leak is treating a symptom. It will be low again, and you will pay again. Insist on a pressure test and leak trace.

4. A failed run capacitor

Cost to fix: low. The capacitor gives the compressor and fan motors the kick they need to start. When it weakens, the compressor may hum, struggle, or fail to start at all while the fan keeps turning - so the unit appears to be running while producing no cooling whatsoever.

It is an inexpensive part and a quick replacement. It is also a part that degrades with heat and age, which is why it shows up so often in older units.

5. The unit is in the wrong mode

Cost to fix: nothing, and mild embarrassment. Set to Fan, it blows room-temperature air. Set to Dry, it dehumidifies with minimal cooling. Set to Heat in winter and forgotten about, it will cheerfully do the opposite of what you want.

Check the remote before you check anything else. We have driven across town for this.

6. Airflow problems in a ducted system

Cost to fix: varies. If one room is warm and the rest are fine, the problem is distribution, not the unit. Crushed or kinked flexible duct, a disconnected branch, a closed damper, or a system that was never balanced after installation.

This is extremely common in homes where ducting was installed quickly and never commissioned properly. Read more on .

7. Compressor failure

Cost to fix: significant. The expensive end of the list, and thankfully the rarest. The compressor is the pump at the heart of the system. When it fails, the choice is usually between a major repair and replacing the unit.

If the unit is over ten years old and runs on R22 refrigerant, replacement is almost always the better decision - R22 is phased out, the gas is scarce and expensive, and a modern inverter will cut your running costs substantially.

What to do right now

1. Check the mode on the remote.
2. Wash the filters and run it again for an hour.
3. Look at the outdoor unit - is the fan spinning, and can you see clean metal between the fins?
4. If it is icing up, tripping the breaker or dripping water, switch it off at the isolator and call.

Our free troubleshooter walks you through the symptoms interactively, and tells you how urgent each one is. If you would rather we just sorted it, book a visit or call 076 537 8987.