Air Conditioner Not Cooling? Here's What to Do

It's the middle of a Sydney summer and your split system or portable air conditioner is running but not actually cooling the room. This is frustrating — but before calling a technician or buying a replacement, there are several things you can check yourself.

1. Check the Filter is Clean

A dirty filter is the number one cause of poor cooling performance. When the filter is clogged with dust, airflow is restricted and the AC can't move enough air to cool the room effectively.

Fix: Turn off the unit, remove the front panel, and slide out the filter. Wash it under running water, let it dry completely, and reinstall. Run the AC again and see if cooling improves.

2. Make Sure It's Set to 'Cool' Mode

Split systems have multiple modes: Cool, Heat, Fan, Dry, and Auto. If it's accidentally set to Fan or Dry mode, it will run but not refrigerate the air.

Fix: Press the Mode button on the remote until the snowflake (❄️) icon appears, confirming Cool mode is active.

3. Set the Temperature Low Enough

If your set temperature is 25°C and the room is already at 24°C, the AC won't engage the compressor because it thinks the target is reached.

Fix: Set the temperature to at least 2–3 degrees below the current room temperature.

4. Check the Outdoor Unit is Running

The outdoor unit (compressor) is the part that actually does the cooling work. If it's not running while the indoor unit is on, the system won't cool.

What to look for: The outdoor unit fan should be spinning. If it's completely still and silent, the compressor isn't engaging — this may indicate a faulty compressor, low refrigerant, or a tripped thermal cut-out.

5. Check for Ice Buildup

Paradoxically, an air conditioner can freeze up and produce no cold air because of a blocked filter, low refrigerant, or running in very cold weather. Ice on the indoor coils blocks airflow.

Fix: Turn the AC to Fan Only mode for 30–60 minutes to let the ice melt. Check the filter and clean if needed. If it freezes again, call a technician — low refrigerant may be the cause.

6. Check the Room Isn't Too Large

Air conditioners are rated in kilowatts for a reason. A 2.5kW unit simply cannot cool a large open-plan room. If the room is significantly bigger than the AC's rated capacity, it will run constantly but never reach the set temperature.

Rule of thumb: Allow approximately 0.1 kW per square metre for a standard room with average insulation.

7. Refrigerant May Be Low

If none of the above fixes work and the AC blows air that's slightly cool but not properly cold, it may have low refrigerant (gas). This requires a licensed refrigeration mechanic — it's not a DIY fix.

When to Replace vs Repair

If your AC is over 10 years old and needs a refrigerant recharge or compressor replacement, the repair cost can easily exceed the value of the unit. At that point, it's worth considering a replacement.

Oceania Appliances stocks quality used split systems and portable air conditioners at great prices. Call us on 0481 243 211 to find out what's available, with free delivery across Sydney.