Few things are worse in Singapore than an aircon that runs all night without actually cooling the room. Before you assume the worst, it helps to know that many causes are simple — and some can be checked in a couple of minutes.

Quick checks before you call anyone

  • Check the mode. Make sure the remote is set to Cool (snowflake icon), not Fan, Dry or Auto.
  • Check the temperature. Set it to 24–25°C. Setting 16°C will not cool faster — it just makes the unit work harder.
  • Replace the remote batteries. A weak remote may not be sending your settings.
  • Close doors and windows and draw the curtains on sun-facing windows.
  • Check the outdoor unit is running and that nothing is blocking it.

Still not cold? Here are the eight most common causes.

1. Dirty air filters

The most common cause by far. Clogged filters choke airflow, so less cool air reaches the room. Wash them every 2 to 4 weeks.

2. Dirty evaporator coil

Dust and mould on the coil act like insulation, stopping it from absorbing heat. A chemical wash usually restores cooling immediately.

3. Dirty or blocked condenser

The outdoor unit releases heat outside. If its coil is dusty or it is boxed in by items on the AC ledge, it cannot get rid of heat efficiently and cooling suffers.

4. Low refrigerant (gas)

If there is a leak, there is not enough refrigerant to carry heat out of your room. Signs include warm air, ice on the copper pipes and a hissing sound. The leak must be found and fixed before a gas top-up.

5. Faulty capacitor

Capacitors help start the compressor and fan motors. When one fails, the outdoor unit may hum but not run, so you get airflow without cooling. This is a quick, affordable repair.

6. Faulty sensor or PCB

If the temperature sensor misreads the room, the system may stop cooling too early. Blinking lights or error codes often point to sensor or PCB issues.

7. Wrong aircon size for the room

An undersized unit will run constantly and never quite cool a large or sun-facing room. This is common after renovations that combine rooms. We cover BTU sizing in our aircon buying guide.

8. Ageing compressor

Compressors wear out over time. If your system is over 10 years old and needs repeated repairs, replacement is often better value than another fix.

When to call a technician

Call us if the quick checks do not help, if you see ice on the pipes, hear unusual noises, see error codes, or if the outdoor unit is not running. Running a faulty aircon for long periods can turn a small repair into a big one.

Aircon not cold? Our technicians diagnose the actual cause first and give you a clear quote before any work begins. The diagnosis fee is waived if you go ahead with the repair.