TL;DR — Quick Answer
- The most common culprit is a clogged air filter — clean it first before calling anyone.
- If that doesn't help, you likely have a refrigerant (gas) leak or dirty coils that need a technician.
- If the fan runs but there's zero cooling, suspect a compressor fault.
- Most cases are fixed with a general service or chemical overhaul — usually under $150.
Your aircon is running, the fan is blowing, but the room just isn't getting cold. It's one of the most frustrating situations in Singapore's heat — and it's also the number one complaint we hear from homeowners and tenants across HDB flats and condos.
The good news: this problem almost always has a clear cause. Here are the 7 most common reasons your aircon is not cold, and what you should do about each one.
1. Dirty or Clogged Air Filter
Start here — always. The air filter catches dust, pet hair, and airborne particles every single day. When it clogs up, airflow is choked and the unit has to work significantly harder just to push the same amount of cool air into your room.
Signs: Weaker airflow than usual, musty smell when the unit turns on, room takes much longer to cool.
Fix: Remove the filter panel (usually snaps open from the front of the indoor unit), rinse the filter under running water, let it dry completely, and reinstall. In Singapore's dusty climate, do this every 3 to 4 weeks. It takes 10 minutes and costs nothing.
💡 Pro Tip
Set a recurring phone reminder every 3 weeks to check your filter. This one habit prevents the majority of aircon "not cold" complaints and extends your unit's lifespan considerably.
2. Low Refrigerant (Gas Leak)
Refrigerant is the substance that actually makes your aircon cold — it absorbs heat from inside your room and releases it outside. If the refrigerant level is low due to a slow leak in the piping, your aircon physically cannot cool the air properly regardless of how long it runs.
Signs: The unit runs continuously but the room stays warm. Ice forming on the indoor unit or copper pipes. A faint hissing sound near the indoor or outdoor unit.
Fix: This requires a licensed technician. They need to locate and repair the leak, then top up the refrigerant to the correct level. Simply topping up gas without fixing the leak is money wasted — it will run low again within a few months.
3. Dirty Evaporator Coils
Even if you clean your filter regularly, dust still finds its way onto the evaporator coils behind the filter over time. A layer of grime on these coils acts as insulation and prevents proper heat exchange, killing cooling efficiency.
Fix: A professional chemical wash or chemical overhaul cleans the coils thoroughly. In Singapore, this is recommended at least once a year — more often if the unit runs 8 or more hours daily.
4. Blocked or Dirty Outdoor Unit
The outdoor condenser unit releases the heat that your aircon pulls out of the room. If it's surrounded by plants, blocked by stored items, or caked in grime, it can't do its job — and your indoor unit suffers for it.
Check: Make sure there's at least 30cm of clearance around all sides of the outdoor unit. If the fins look dirty or blocked, call a technician to clean the condenser coils.
5. Thermostat or Remote Settings
This sounds obvious, but it is a genuinely common cause that gets overlooked. Check that the mode is set to "Cool" and not "Fan Only" or "Dry" mode. Also verify the set temperature is actually lower than the current room temperature — if someone set it to 28°C on a 28°C day, the aircon has nothing to work toward.
If the remote isn't responding correctly or the display is acting oddly, replace the batteries first. A faulty remote signal can prevent the unit from switching to the proper mode.
6. Undersized Unit for the Room
An aircon that is too small in capacity for the room it is cooling will run constantly and still fail to bring the temperature down. This is a sizing problem from the original installation, not a fault that developed over time.
The rule of thumb in Singapore is roughly 8,000 BTU for a standard 100-120 sq ft bedroom, and around 12,000-14,000 BTU for a larger living room. If your unit is undersized, consult a technician about upgrading or adding a supplementary unit. See our installation guide for more on choosing the right system size.
7. Compressor Failure
The compressor is the engine of the entire aircon system. When it fails, the fan may still run and the unit may still turn on — but there will be absolutely no cooling at all. Compressor failure is usually a sign of an older unit, long-term refrigerant neglect, or an electrical fault.
Signs: Fan runs normally but zero cold air. Clicking sound when the compressor tries to start. Unit trips the circuit breaker when turned on.
Fix: Compressor replacement is expensive — sometimes approaching the cost of a new unit. A certified technician should assess whether repair or full replacement is the more sensible financial decision for your situation. For older units, a reconditioned second-hand unit can be a very cost-effective alternative.
"If your aircon hasn't been serviced in over a year and suddenly stops cooling, a professional service call will fix it in the vast majority of cases. Don't delay — running a struggling aircon puts enormous strain on the compressor."
When to Call a Technician
Try cleaning the filter yourself first. If that doesn't solve it within a day of running the unit, call a professional. Definitely call immediately if you notice any of these:
- Ice forming on any part of the indoor unit or copper pipes
- Water leaking from the indoor unit (separate from the drain pipe)
- Unusual sounds — clicking, banging, or hissing
- A burning smell from the unit
- The unit trips your circuit breaker when switched on
K2L Aircon provides same-day aircon repair across Singapore. We diagnose the problem first and tell you the cost before we do anything. WhatsApp us for a free assessment.