Over time, the filter gets coated in dust, pet hair, and airborne particles. When blocked, it restricts the airflow across the evaporator coil — and without enough airflow, the unit simply can't transfer heat effectively out of your room.
How to tell: Reduced airflow from the vents, musty smell, and unit may feel like it's working harder than usual. If you pull out the filter and it's grey and thick with dust, that's your answer.
Refrigerant is the substance that actually absorbs heat from your room and transfers it outside. If your unit has a slow refrigerant leak, the system loses its ability to cool — the air blows, but there's nothing to extract the heat with.
How to tell: The unit blows air at near-ambient temperature. You may notice ice or frost forming on the indoor unit or the copper pipes outside. The unit runs continuously but the room doesn't cool down. There may be a faint hissing sound near the indoor unit.
The evaporator coil (inside unit) absorbs heat; the condenser coil (outside unit) releases it. Both can get coated in dirt, mould, or grime over time, insulating the coils and dramatically reducing their efficiency. This is one of the most underappreciated causes of poor cooling.
How to tell: The unit has been running for years with only occasional servicing. Visible grime or mould on the indoor unit's fins. The outdoor unit's coil has leaves, dust, or debris clogging it.
If your aircond was installed years ago in a smaller room that's since been extended, or if it was undersized at installation, it will run constantly but never quite cool the space. A 1HP unit is typically suitable for rooms up to about 150 sq ft; a 1.5HP unit for up to 250 sq ft.
How to tell: The unit runs non-stop with the thermostat at its lowest setting, but the room takes 45+ minutes to cool down, or never reaches a comfortable temperature.
Modern airconds are controlled by a PCB (printed circuit board) that regulates temperature, compressor speed, and fan settings. If the thermostat sensor is faulty or the PCB has a fault, the unit may run but not engage the cooling cycle properly — or may shut the compressor off too early.
How to tell: The remote shows the correct temperature but the unit doesn't respond normally. The unit cycles on and off rapidly. The compressor (outdoor unit) isn't running even though the indoor fan is on.
The outdoor condenser unit needs space around it to expel heat effectively. If it's boxed in by walls, covered by overgrown plants, or located in a hot enclosed space with no airflow, it will struggle to reject heat — and the indoor unit will lose cooling capacity as a result.
How to tell: The outdoor unit feels excessively hot to the touch, even compared to a warm day. There's reduced airflow from the outdoor unit's fan. The unit performs better in the evening or on cooler days than in the afternoon heat.
Not sure what's causing your aircond to underperform?
WhatsApp us your unit model, room size, and what you're experiencing — we'll tell you the most likely cause and whether it needs a technician.
WhatsApp for Free AssessmentCan I Fix a Poorly Cooling Aircond Myself?
Of the six causes above, a dirty air filter is the one you can address yourself — and it's also one of the most common. Clean it regularly (every 4–6 weeks in a dusty environment), and you'll eliminate one of the top reasons for poor cooling. Some homeowners also clear debris from around the outdoor unit, which is safe and easy to do.
Everything else on this list — refrigerant, coil cleaning, PCB faults, or upsizing — requires a professional with the right tools. Attempting to handle refrigerant yourself is dangerous and illegal in Malaysia without a license.
Why Does My Aircond Sometimes Cool Well and Sometimes Not?
Inconsistent cooling is often a sign of a developing problem rather than a sudden failure. Common culprits include a refrigerant leak that's slow (so the gas level drops gradually), a dirty coil that's worse in peak afternoon heat, or a PCB issue that intermittently affects the compressor. If your aircond performs well in the morning but poorly in the afternoon, that's a strong clue — the outdoor unit may be overheating, or the system is struggling under higher ambient temperatures.
Quick Summary: 6 Reasons Your Aircond Isn't Cooling
- Dirty air filter — most common; clean every 4–6 weeks
- Low refrigerant — needs professional leak fix + gas top-up
- Dirty coils — chemical wash resolves this
- Undersized unit — may need upgrade or room changes
- PCB/thermostat fault — requires diagnosis and repair
- Blocked outdoor unit — clear 50cm of space around it