A well-functioning split-unit aircon in Singapore should cool a standard bedroom to target temperature within 20 to 30 minutes. If yours has been running for 45 minutes and the room still feels warm, something is off. Slow cooling is almost never a quirk of the system, but a symptom.
And when your aircon is not cool the way it used to be, the cause is usually one of five things: a dirty filter, contaminated coils, low refrigerant, a unit that's undersized for the space, or a room that leaks cool air faster than the unit can produce it.
The filter sits behind the front panel of the indoor unit, trapping dust before it reaches the coils. In Singapore's humidity, it clogs fast, often within two to four weeks of daily use. When airflow drops, less air passes over the cold coils, and what reaches the room feels weak.
Cleaning the aircon filter is something you can handle yourself. Slide the filter out, rinse it under cool tap water, let it dry completely, and slot it back in. If the room still cools slowly afterwards, the problem lies deeper in the unit.
Behind the filter sit the evaporator coils. Outside, in the condenser, there's a second set. Both transfer heat: the evaporator absorbs heat from your room, the condenser releases it outdoors. When either surface is coated in dust, grease, or biofilm, that transfer slows dramatically.
Evaporator coils sit deep inside the fan coil unit, wrapped around delicate fins, and cannot be cleaned with a cloth. Proper cleaning requires dismantling the unit and flushing the coils with chemical solvent, which is what an aircon chemical wash does. At this stage, it’s best to engage a qualified aircon specialist. A chemical overhaul goes further, stripping the blower, drain pan, and internal components for a deep clean.
If your unit has gone 12 months or more without one, that's almost certainly why you may have issues with your aircon not cooling now.
Refrigerant is the chemical that actually does the cooling. If levels drop below spec, the system loses its ability to move heat, and the air coming out of your vents gets progressively less cold.
The usual signs, beyond slow cooling:
A sealed aircon system should not lose refrigerant. If levels are low, there's a leak somewhere. A gas top-up on its own is a temporary patch. Anyone who tops up your gas without checking for a leak is costing you more than they're saving.
Every aircon is rated in BTU (British Thermal Units), which measures how much heat it can remove per hour. If the aircon BTU rating is too low for the room, the compressor runs continuously without ever hitting target temperature.
A rough guide for Singapore homes:
West-facing rooms, floor-to-ceiling glass, kitchens, and open layouts need 10% to 20% more BTU than the baseline. If your aircon runs flat out and still can't beat the room, no amount of servicing will fix it. The unit needs to be replaced with a correctly sized one.
Cool air escapes, warm air enters, and the faster either happens, the harder your aircon works. Common leak points:
None of these are aircon faults. They're room faults. Before booking a service, close the door, draw the curtains, shut the windows, and run the unit for 30 minutes. If the room cools properly, your aircon is fine.
Filters and room sealing are DIY. Coil contamination, refrigerant loss and incorrect sizing are not. Running an aircon unit that’s blowing warm air in the hope it sorts itself out accelerates compressor wear, the single most expensive replacement part in any aircon system. If you've cleaned the filter, sealed the room, and the unit still won't cool properly, it’s time to get it diagnosed.
81 Aircon is a long-established aircon servicing company in Singapore, offering BCA-registered technicians who will inspect your unit, identify where the issue lies, and give you a quote before any work begins. Book a free site consultation with us today.
