Are you facing an aircon not cooling? 8 causes and how to fix them will be covered in this definitive guide. Your aircon is running, but the room is still stuck at a sweltering 31°C.
We see this frustrating scenario every day. At Coolbest Aircon Servicing, our mission is to deliver reliable, high-quality cooling solutions to communities across Singapore at affordable prices. A hot room usually points to a few specific hardware failures or simple setting errors.
This ordered diagnostic will help you troubleshoot the problem effectively. You can resolve half of these issues in under five minutes without any tools. Before you contact a technician, run through these quick steps.
Aircon Not Cooling? 8 Causes and How to Fix Them: Fast 30-Second Checks First
Before opening any panels, verify the absolute basics. Our technicians frequently resolve breakdowns that are actually just simple configuration errors. The most common culprit is selecting the wrong mode on the remote.
- Remote is on “Cool” mode: Look for the snowflake icon. The water droplet icon means “Dry” mode, which reduces humidity but cools the room very slowly.
- Temperature setting below room temp: Set the remote to 22°C. Setting it to 28°C will not force the compressor to activate.
- No object blocking airflow: Ensure curtains or furniture do not block the indoor unit.
- Outdoor unit is actually running: Step outside to verify the large fan is spinning.
If all four checks pass, proceed to the specific causes below.
Cause 1: Dirty Air Filter (DIY, 15 min fix)
A clogged air filter is the most common reason for weak airflow. We always check this first during any service call. A dirty mesh traps cold air inside the unit, causing the coil to freeze and stopping the cooling process entirely.
According to a 2026 report by SuperClean SG, neglecting your filter reduces energy efficiency by up to 15%.
Fixing a Dirty Filter
Lift the front cover of your indoor unit. Slide out the plastic mesh filters carefully. Rinse them under cool tap water from back to front to push dust out.
Never use harsh detergents or scrub brushes. Let the filters air-dry for two hours before refitting them. Turn the unit back on and wait 20 minutes for cool air to return.
Cause 2: Incorrect Remote Mode Or Temp Setting
Many users accidentally switch modes while fumbling with the remote in the dark. Our team notices this frequently with Mitsubishi and Panasonic remotes featuring tiny buttons. The Dry mode reduces humidity but runs the compressor at low speeds, preventing rapid cooling.
Resetting the Remote
Check the display for the snowflake icon representing cool mode. Change the fan speed to “Auto” or “High” instead of low. Set the temperature to 22°C.
Wait 15 minutes to see if the room temperature drops. The compressor needs this time to engage and circulate the refrigerant properly.
Cause 3: Low Refrigerant or Leak (Technician, same day)
An aircon blowing warm air briefly before turning hot usually indicates a refrigerant leak. We often spot ice forming on the copper pipes outside or hear a faint hissing sound. Refrigerant never simply gets used up over time. A low gas level always means a leak exists somewhere in the copper piping.
Refrigerant Costs in Singapore
A simple top-up without fixing the leak will only last a few weeks. You need a licensed technician to pressure-test the system, locate the leak, and seal it. Different gases carry different replacement costs based on 2026 Singapore pricing data.
| Refrigerant Type | Average Top-Up Cost (S$) | Characteristics |
|---|---|---|
| R32 | S$80 to S$200 | High efficiency, mildly flammable |
| R410A | S$60 to S$150 | Standard for mid-age residential units |
| Leak Seal Repair | S$100 to S$200 | Essential to prevent future gas loss |
Cause 4: Iced-Over Evaporator Coil (Technician, same day)
Opening the front cover and seeing a block of ice on the aluminium fins means airflow is severely restricted. Our specialists know this happens due to a filthy filter or low refrigerant. The ice blocks the cold air from entering your room.
Thawing the Coil
Do not try to melt the ice with a hairdryer. The intense heat will permanently warp the delicate aluminium fins. Turn the aircon to Fan only mode for two hours.
This allows room temperature air to slowly melt the buildup. Call a technician to diagnose the root cause once the ice melts.
Cause 5: Faulty Thermostat or Thermistor (Technician)
The thermistor acts as the temperature sensor for your aircon. We find that a failing thermistor sends incorrect data to the control board. The unit will either cycle on and off every minute or run endlessly without ever cooling the room properly.
Diagnosing the Sensor
A technician will use a multimeter to check the resistance of the thermistor. A normal Daikin indoor thermistor reads around 20 kiloohms at 25°C. If the resistance falls outside this range, the sensor requires replacement.
Parts cost between S$90 and S$160 in Singapore. The repair process typically takes about 30 minutes.
Cause 6: Blocked Condenser Unit Outdoors (DIY, 10 min)
Outdoor condenser units need adequate breathing room to dissipate heat. Our technicians frequently see HDB service balconies cramped with drying laundry or boxes. Housing and Development Board regulations strictly prohibit placing objects on the aircon ledge, as this blocks airflow and creates a fire hazard.
Clearing the Condenser
Clear at least 30cm of empty space around the outdoor unit in all directions. Use a garden hose to gently wash down the exposed metal fins from the outside.
Do not use a high-pressure washer, as this bends the fins. Wait 20 minutes after washing before testing the cooling performance.
Cause 7: Compressor Failure (Technician, major)
A broken compressor is the most severe mechanical failure your system can suffer. We consider this the heart attack of the air conditioning unit. You might hear a loud, sustained hum followed by a click, or the circuit breaker might trip within 60 seconds of switching the power on.
Repair vs Replacement Costs
Sometimes the issue is just a blown capacitor. This cheap fix ranges from S$100 to S$160.
A full inverter compressor replacement costs between S$500 and S$1,000 in Singapore. At that price point, replacing the entire condensing unit often makes more financial sense.
Cause 8: PCB Fault (Technician, replacement)
The Printed Circuit Board serves as the main brain of your air conditioning system. Our diagnostic tests confirm a PCB fault when the unit ignores remote commands, gets stuck on one fan speed, or flashes continuous error codes. Moisture or power surges typically cause these boards to short out.
PCB Replacement Expectations
Replacing a standard residential PCB costs between S$350 and S$900 in Singapore. Premium commercial systems carry even higher repair fees. Daikin VRV control boards can exceed S$1,000 to replace.
Urgency Guide, When To Call
Knowing when to seek immediate help prevents minor issues from destroying expensive hardware. We use a simple triage system to prioritise service calls. Delaying a repair on a tripping breaker can cause electrical fires.
| Symptom | Urgency Level | Required Action |
|---|---|---|
| Warm air, clean filter, normal remote | Same-day diagnostic | Check refrigerant levels |
| Ice on copper pipes | Same-day | Thaw system and diagnose leak |
| Hissing sound near outdoor unit | Same-day | Suspected refrigerant leak |
| Loud compressor hum, tripping breaker | Today | Shut off power immediately |
| Blinking error code, won’t start | Today | Record the specific blink pattern |
| Slight cooling, hot weather | Next-day | General servicing required |
What To WhatsApp Us
Providing clear information upfront helps us diagnose the problem faster. We can often prepare the exact replacement parts before arriving at your home. Please send us a few key details to expedite the process.
- Photo of the aircon model sticker: Locate this on the side panel of the indoor unit.
- Short video of the symptom: Show the warm air blowing while the remote displays “Cool” mode.
- Photo of any error codes: Capture any blinking indicator lights on the indoor unit.
- Any ice on the pipes: Check the copper connections outside for white frost.
If you are facing an aircon not cooling? 8 causes and how to fix them are exactly what our team handles daily. Reach out, and we will restore your comfort quickly.
Book an aircon repair, available same-day in the West Region and next-day elsewhere.