Why Is My Aircon Not Cold? 7 Common Causes (And Fixes)

It's 33°C outside, the aircon's running, and the room feels like someone left a fan on instead. Sound familiar? In 34 years of fixing aircons in Singapore, here are the 7 most common causes we see — ranked from cheapest fix to most expensive.

1. Dirty filters (easiest fix — sometimes free)

If your aircon hasn't been serviced in over 4 months, dirty filters are the #1 cause of weak cooling. Filters clogged with dust restrict airflow, so even though the coil is cold, very little air passes through.

Fix: Open the front cover, remove the filters, wash them with mild soap and water, dry completely, reinstall. Takes 15 minutes. If cooling restores, you just saved a service call. If not — keep reading.

2. Iced-up coil (sign of #1 or low gas)

Look at the indoor coil through the louvre. If you see ice or frost on it, the airflow is too restricted (back to dirty filters) OR the refrigerant is low. Switch off the aircon for 1 hour to let the ice melt, then test again.

Fix: Clean filters first. If ice returns within hours, you likely have low gas — call a technician to pressure-test.

3. Low refrigerant gas

Refrigerant doesn't "run out" naturally — it leaks. Common leak points: the flare nuts at the unit, the pipe insulation joins, micro-holes in copper after 10+ years. Just adding gas without fixing the leak is throwing money away — the gas will leak out again in weeks.

Fix: Pressure-test to find the leak first ($30–$60 callout), repair if possible, then top up. Gas top-up alone is $60–$150 per unit depending on type (R22, R410A, R32) and amount.

4. Dirty coil / heat exchanger

A coil caked in dust and bacteria acts like a thermal blanket — heat can't transfer efficiently into the refrigerant, so you get weak cool air. Common after 12+ months without service.

Fix: Chemical wash ($80–$120) for moderate build-up, chemical overhaul ($120–$140) for severe.

5. Outdoor unit (condenser) issues

Move out to the balcony / corridor. Is the outdoor unit's fan spinning? Are there leaves, plastic bags, or bird nests blocking the airflow? Outdoor unit can't dump heat → indoor unit can't cool.

Fix: Clear obstructions. If fan isn't spinning, the capacitor or motor may have failed — needs technician diagnosis ($30 callout).

6. Wrong system size

If your aircon is BTU-undersized for your room (e.g., a 9,000 BTU in a 200 sqft sun-facing master bedroom with a glass window), it will never cool properly. The compressor runs flat-out 24/7 and still loses.

Fix: Sometimes a larger unit is the only real answer. Consult before buying — a home assessment ($30) will confirm if your existing system is right-sized.

7. Compressor failing (worst case)

If everything else checks out — filters clean, gas full, coil clean, outdoor unit working — and cooling is still weak, the compressor itself may be wearing out. For 10+ year old units, this often means it's time to replace rather than repair.

Fix: Honest diagnostic visit. We'll tell you if it's worth fixing or if a new unit makes more financial sense over a 5-year horizon.