Updated 2026-10-11 · AirconList
Short answer: Start with the filters: dirty filters are the most common and cheapest cause. Then check the outdoor unit is running with at least 60 cm of clear space. If it still blows warm, the likely causes are low refrigerant from a leak, a dirty coil, or a failed compressor, capacitor or fan motor, which need a technician.
Check these yourself first
Based on Helpling’s guide to aircon problems (Helpling):
- Filters. Clogged filters are the most common and easiest fix. Helpling suggests cleaning them every 2 to 4 weeks.
- Settings. Mode on cool, temperature set below room temperature, remote batteries working.
- The outdoor unit. Is the fan spinning? Is there at least 60 cm of clear space around it, with no boxes or plants blocking it?
When it is a technician’s job
| Cause | What it involves |
|---|---|
| Low refrigerant | Low levels almost always mean a leak: fix the leak, then recharge |
| Dirty evaporator coil | A chemical wash or overhaul |
| Failed compressor, capacitor, control board or fan motor | Diagnosis and repair; a failed outdoor fan motor is urgent because heat can damage the compressor |
| Wrong size for the room | A correctly sized unit |
What it costs
Helpling lists a diagnostic visit at S$60, waived if the repair is booked, and gas top-up from about S$100 to S$130 a unit depending on the refrigerant (Helpling price list). Ask for a leak check before paying for gas.
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More questions
Do aircons need regular gas top-ups?
No. Refrigerant runs in a sealed loop and is not used up, so low levels almost always mean a leak.
What size aircon does an HDB room need?
Helpling's guideline is about 9,000 BTU for a common room, 12,000 BTU for a master bedroom and 18,000 BTU or more for a living room.