A hot day, the air conditioner is running, and the room is still warm. Before booking a technician it is worth spending a few minutes on simple checks. Some faults you can solve yourself, and in the rest you will be able to tell the technician exactly what is happening.
First: the one-minute checks
- Mode: make sure the remote is set to cooling, not to dry, fan or auto.
- Temperature: set it a few degrees below room temperature. For cooling, 24 to 25 °C is a good starting point.
- Remote batteries: a remote with weak batteries does not always send every command.
- Windows and doors: a unit cooling a room that is open to the rest of the house will struggle to reach the set temperature.
1. Clogged filters
This is the most common cause by far. Dust builds up in the filters, restricts the airflow, and less cold air comes out. In extreme cases ice forms on the coil.
What to do: disconnect the unit from power, open the front cover, take the filters out and rinse them in lukewarm water. Dry them completely before putting them back. We have a full guide to cleaning an air conditioner.
2. A blocked or dirty outdoor unit
The outdoor unit releases the heat your AC removes from the house. If it is blocked by objects, covered in dust or squeezed into an enclosed space, it cannot release that heat and cooling drops off.
What to do: clear objects away from the unit and make sure air can flow around it. Leave cleaning the outdoor coil itself to a technician.
3. The wrong settings
A timer that switched the unit off, a sleep mode that gradually raises the temperature, or an eco mode that caps the output. On modern remotes it is easy to press a button by accident and change how the unit behaves.
What to do: cancel timers and special modes, and reset the remote according to the manufacturer’s instructions if needed.
4. Low refrigerant caused by a leak
An air conditioner does not “use up” refrigerant. If it is low, there is a leak. The usual signs: lukewarm air, ice on the pipework or coil, and sometimes a faint hissing sound.
Worth knowing: topping up refrigerant without finding and fixing the leak is only a temporary fix. This is work for a certified technician.
5. A fan or compressor fault
If the indoor unit runs but the outdoor fan does not turn, or the compressor never starts, the unit will simply blow air at room temperature. Sometimes you hear a buzz or a clicking from the outdoor unit.
What to do: switch the unit off and book an inspection. Repeatedly restarting it can make the damage worse.
6. A capacity that does not match the room
Sometimes the unit is perfectly fine, just too weak for the space. This happens in rooms that were extended, in a living room open to the kitchen, on a top floor, or in a room with large west-facing windows.
What to do: check the recommended capacity in our capacity calculator. If the gap is large, it is worth discussing a replacement or an additional unit.
7. A sensor or control board
A failed temperature sensor can “think” the room is already cool and stop the cooling. A control board fault can cause inconsistent behaviour and error codes on the display.
What to do: photograph the error code, if there is one, and the model sticker, and send them to us. It helps us understand the fault in advance.
When to stop checking and call a technician
- Ice on the coil or pipework that comes back after defrosting
- The outdoor unit never starts, or is very noisy
- The breaker keeps tripping
- A burnt or melting-plastic smell
- The unit still does not cool after cleaning the filters and checking the settings
Safety: do not open the unit covers, and do not touch electrical connections or the refrigerant pipework. Disconnect the power before any cleaning.
Checked everything and it still will not cool?
Tell us what is happening, attach a photo, and we will get back to you. We are available 24/7.
