Aircond Not Cold? 10 Causes and What You Can Check Yourself First

Short answer: when an aircond runs but isn't cold (what Malaysians call "aircond tak sejuk"), the cause is usually a dirty filter or coil, the wrong remote setting, low refrigerant from a leak, or an outdoor unit that has stopped running, often because of a failed capacitor. The first two you can check yourself in minutes. The rest need a technician with gauges and a meter.

5 checks to do before you call anyone

These take less than ten minutes and solve a surprising number of "not cold" calls:

1. Check the mode on the remote. It should show the snowflake (Cool), not Fan, Dry or Auto. Set it to 24°C with the fan on Auto.
2. Pull out the filters. If they're grey and furry, wash them under the tap, let them dry and put them back.
3. Look at the outdoor unit. With the aircond on Cool for five minutes, is the outdoor fan spinning and can you hear the compressor humming? If it's silent, note that for the technician.
4. Check the breaker. Make sure the aircond's breaker in the DB box hasn't tripped.
5. Close up the room. Open windows, a door to the kitchen or strong afternoon sun on a west-facing window can overwhelm a small unit.

If none of that helps, one of the causes below is almost certainly the reason.

The 10 real causes of an aircond not cooling

1. Dirty filter

The most common cause and the easiest fix. A clogged filter chokes the airflow, so less air passes over the cold coil. In KL, bedroom filters used nightly can clog in a few weeks. Wash them every two to four weeks.

2. Dirty cooling coil and blower

Behind the filter, dust and mould coat the coil fins and the blower wheel. Air still blows, but it's weaker and not as cold, and the room takes much longer to cool. Washing the filter won't fix this; it needs a chemical service. If the unit hasn't been cleaned for years, read overhaul vs chemical service.

3. Wrong settings

Dry mode, Fan mode, a timer, or a "quiet" setting can all make a unit feel weak. Some remotes also get left on a high set temperature after someone feels cold at night. Reset to Cool, 24°C, fan Auto before assuming a fault.

4. Low refrigerant gas from a leak

If the air is cool but never cold, and you see frost or ice on the small copper pipe at the outdoor unit, the gas is probably low. Gas doesn't get used up, so low gas means a leak, usually at a flare joint or the coil. Topping up without fixing the leak just buys a few weeks. Our gas topup always starts with a leak check.

5. Failed capacitor (outdoor unit not starting)

One of the most common faults we see in KL heat. The capacitor gives the compressor and outdoor fan the kick they need to start. When it weakens, the indoor unit blows air but the outdoor unit stays silent or hums without starting, so the air comes out at room temperature. It's a relatively cheap part, but it must be replaced by a technician because it stores an electrical charge.

6. Faulty outdoor fan motor

If the compressor runs but the outdoor fan doesn't spin, heat can't be removed and the unit soon overheats and cuts out. You'll often notice the outdoor unit very hot to the touch with the fan still or turning slowly.

7. Blocked or badly placed outdoor unit

Outdoor units squeezed into a narrow ledge, facing a wall, or sitting in direct afternoon sun breathe their own hot air back in. Road dust and leaves clog the condenser coil too. The unit works harder and cools less. Cleaning the condenser helps; sometimes relocating it is the real fix.

8. Sensor or circuit board fault

Inverter units rely on temperature sensors and a control board. A faulty sensor can make the unit think the room is already cold, so it slows down. Blinking lights or an error code on the indoor display point here. A code is a starting point for diagnosis, not automatically a new board.

9. Unit too small for the room

If the aircond has never cooled the room properly, even when new, it may simply be undersized. A 1HP unit can't keep up with a 300 sq ft living room. Check our aircond HP size guide to see what your room needs.

10. Worn compressor

On old units, the compressor itself can lose efficiency or fail. This is the most expensive repair, and on a unit more than ten years old, especially one still running R22 gas, replacing the aircond is often better value. We'll tell you honestly which makes sense.

When to switch it off and call straight away

• The outdoor unit is completely silent, or hums but doesn't start
• There's ice on the pipes or the indoor coil
• The breaker trips when the aircond starts
• You smell burning or see scorch marks near the unit or the plug
• Water is dripping from the indoor unit at the same time (see aircond leaking water)

Running a unit in these conditions can turn a small repair into a compressor replacement.

How much does it cost to fix an aircond that's not cold?

Full repair pricing by unit type is on our aircond repair page.

Still not cold?

WhatsApp Marvel a short video of the indoor and outdoor unit running, plus the brand and model if you can see it. In many cases we can narrow down the cause before we arrive, so the visit is short and the price is clear before any work starts.