An aircon that is running but Aircon not cold may have an incorrect remote setting, a dirty air filter, restricted airflow, a dirty cooling coil, a refrigerant leak, a frozen evaporator coil, or a faulty component. Start by selecting Cool Mode, setting the temperature to 23–25°C, and cleaning the filter. If the air remains warm after 15–20 minutes, arrange a professional inspection.
An aircon not cooling properly is especially uncomfortable in Singapore’s hot and humid climate. However, weak cooling does not automatically mean the system needs a gas top-up. The correct solution depends on the symptoms and the actual fault.
This guide explains why your aircon is not cold, what you can check safely, and when you need professional aircon repair in Singapore.
Why Is My Aircon Not Cold?
Your aircon may not be cold because it cannot absorb heat effectively, circulate enough air, or release heat through the outdoor unit.
The most common causes are:
- Incorrect remote-control settings
- Dirty air filters
- Dirty evaporator coil or blower
- Blocked outdoor condenser
- Refrigerant leakage
- Frozen evaporator coil
- Faulty temperature sensor
- Fan motor failure
- Compressor or PCB problems
- Insufficient cooling capacity
The symptom pattern can help identify the likely cause.
| Symptom | Possible cause | Recommended action |
|---|---|---|
| Air blows but is not cold | Wrong mode, dirty coil, or refrigerant fault | Check settings, then arrange inspection |
| Air is cold, but airflow is weak | Dirty filter, blower, or frozen coil | Clean the filter and inspect the fan coil |
| Ice appears on the copper pipe | Airflow or refrigerant problem | Switch off and call a technician |
| Only one indoor unit is not cold | Indoor-unit fault | Inspect the affected fan coil |
| All indoor units are not cold | Outdoor unit or system-wide fault | Inspect the condenser and controls |
| Cold at night but warm during the day | High heat load or insufficient capacity | Check sizing, sunlight, and room conditions |
| Cooling returns briefly after gas top-up | Refrigerant leakage | Locate and repair the leak |
| Outdoor unit is not running | PCB, wiring, fan, or compressor fault | Professional diagnosis is required |
Quick Checks When Your Aircon Is Not Cooling
Perform these simple checks before booking a repair. Stop immediately if the aircon is leaking heavily, repeatedly tripping the circuit breaker, or producing a burning smell.
Check Cool Mode and Temperature
Confirm that the remote control is set to Cool Mode, normally shown by a snowflake symbol.
Fan Mode only circulates room-temperature air. Dry Mode mainly reduces humidity and may not provide the strong cooling expected from Cool Mode.
Set the temperature between 23°C and 25°C, select medium or high fan speed, and wait approximately 15–20 minutes.
Setting the temperature to 16°C does not necessarily make the room cool faster. It mainly tells the aircon to continue operating until it reaches a lower temperature.
Also check whether these settings are active:
- Fan Mode
- Dry Mode
- Sleep Mode
- Eco Mode
- Timer
- Quiet Mode
Return the system to normal Cool Mode before testing again.
Check the Remote-Control Batteries
Weak batteries may prevent the remote control from sending commands correctly. The display may still appear normal even when the signal is weak.
Replace both batteries with a matching new pair. Point the remote directly towards the indoor unit and confirm that the aircon acknowledges the command.
If the unit does not respond, the remote control or indoor receiver may require checking.
Clean the Air Filter
A dirty filter restricts airflow. The aircon may still run, but less cold air reaches the room.
Switch off the unit, open the front cover and remove the washable filters. Rinse them gently with clean water and let them dry completely before reinstalling them.
Do not operate the aircon without its filters. If cooling remains weak after cleaning, the evaporator coil or blower may also be dirty.
Regular general aircon servicing in Singapore can help maintain airflow and identify developing problems.
Close Doors and Windows
Open doors and windows allow cooled air to escape while warm, humid air enters. This increases the heat load and makes the aircon appear less effective.
Close the room while testing the aircon. Use curtains or blinds to reduce direct afternoon sunlight and make sure furniture does not block the indoor airflow.
If the room cools at night but remains warm in the daytime, sunlight, poor insulation, or insufficient aircon capacity may be responsible.
Check the Indoor Airflow
Place your hand near the indoor-unit outlet.
If the air feels cold but the airflow is weak, possible causes include:
- Dirty air filter
- Dirty blower wheel
- Dirty evaporator coil
- Frozen coil
- Faulty indoor fan motor
- Obstructed air outlet
Do not insert objects through the air outlet. The rotating blower can cause injury and may be damaged.
Check Whether the Outdoor Unit Is Running
The outdoor unit normally releases heat removed from the room. If its fan or compressor is not operating, the indoor unit may blow room-temperature air.
From a safe location, check for:
- Outdoor fan movement
- Normal operating sound
- Unusual vibration
- Loud buzzing or clicking
- Error lights
- Obstructions around the condenser
Do not open the outdoor unit or touch electrical parts. Outdoor units installed on external ledges or brackets must only be accessed by trained personnel.
10 Common Reasons Your Aircon Is Not Cold
1. Incorrect Remote Settings
Incorrect remote settings are among the easiest aircon cooling problems to correct.
The aircon may be set to Fan, Dry, or Auto Mode instead of Cool Mode. A timer or energy-saving setting may also stop the compressor earlier than expected.
Select Cool Mode, set 23–25°C, choose medium or high fan speed, and wait 15–20 minutes before evaluating the result.
If the unit still blows warm air, continue with the remaining checks.
2. Dirty Air Filter
A dirty air filter reduces the volume of air passing through the evaporator coil. The room then takes longer to cool, and the aircon may operate continuously.
Signs include:
- Weak airflow
- Dusty smell
- Longer cooling time
- Uneven room temperature
- Ice forming inside the unit
Clean reusable filters regularly. If the filter becomes damaged or cannot be cleaned properly, replace it with a suitable filter for the model.
3. Dirty Evaporator Coil or Blower
The evaporator coil absorbs heat from indoor air, while the blower distributes cooled air around the room.
Dust, mould, and grime can reduce heat transfer and airflow. A normal filter wash may not clean contamination deeper inside the fan coil.
Possible symptoms include:
- Weak airflow
- Musty smell
- Aircon not cold enough
- Water dripping
- Uneven airflow
- Higher electricity consumption
Light contamination may be handled through general servicing. Heavy contamination may require an aircon chemical wash or chemical overhaul after inspection.
4. Dirty or Blocked Outdoor Unit
The outdoor condenser releases heat into the surrounding air. Dirt, debris, or restricted ventilation can reduce this process.
Possible signs include:
- Aircon becomes less cold after running for some time
- Outdoor unit feels unusually hot
- Compressor repeatedly stops and restarts
- Cooling is worse during the hottest part of the day
- Outdoor fan is obstructed or not operating correctly
Keep the surrounding area clear, but do not climb onto ledges or attempt to wash an inaccessible condenser yourself.
A technician can inspect the coil, fan motor, capacitor, and compressor operation safely.
5. Refrigerant Leakage
Refrigerant transfers heat between the indoor and outdoor units. A properly sealed aircon system does not normally require regular gas top-ups.
If the refrigerant level is low, the system may have a leak or another issue requiring diagnosis.
Possible signs include:
- Air blows but is not cold
- Ice on copper piping
- Hissing sound
- Longer cooling time
- Aircon runs continuously
- Cooling improves temporarily after a gas top-up
Adding refrigerant without locating the leak may provide only temporary improvement. A technician should test the system, identify the cause, repair it where possible, and charge the correct refrigerant according to the equipment requirements.
6. Frozen Evaporator Coil
A frozen evaporator coil cannot absorb heat correctly. When the ice becomes thicker, airflow and cooling performance fall further.
Common causes include:
- Dirty air filter
- Dirty evaporator coil
- Restricted airflow
- Indoor fan problems
- Refrigerant-system fault
- Sensor or control problem
Switch off the aircon and allow the ice to thaw naturally. Do not scrape the coil or use sharp objects.
If the ice returns, arrange a professional inspection. Repeated freezing can lead to water leakage when the ice melts. See our guide to aircon leaking water if indoor dripping occurs.
7. Faulty Thermistor or Sensor
A thermistor measures temperature and helps the control system regulate cooling.
If the sensor is faulty, loose or incorrectly positioned, the aircon may:
- Stop cooling too early
- Run irregularly
- Display an error code
- Switch on and off frequently
- Produce inconsistent room temperatures
A technician can test the thermistor’s resistance, positioning, wiring, and communication with the PCB.
Replacing a sensor should only be recommended after confirming the fault. Similar symptoms can also arise from airflow, refrigerant, or control-board problems.
8. Indoor or Outdoor Fan Motor Problem
The indoor fan moves cooled air into the room. The outdoor fan removes heat from the condenser.
A weak or failed fan motor may cause:
- Little or no indoor airflow
- Outdoor unit overheating
- Intermittent cooling
- Unusual humming or rattling
- Fan starting slowly
- System shutting down for protection
Switch off the system if the fan produces abnormal noise or does not rotate correctly. Fan motors, bearings, capacitors, and wiring require professional diagnosis.
9. Compressor or PCB Problem
The compressor circulates refrigerant through the cooling system. The PCB controls communication and operation between components.
Possible signs of compressor or PCB trouble include:
- Indoor unit runs, but outdoor unit does not start
- Aircon is completely unable to cool
- Repeated circuit-breaker trips
- Blinking indicator lights
- Outdoor unit starts and stops unexpectedly
- Burning smell or electrical noise
- Error code displayed
Do not repeatedly reset a unit that trips the circuit breaker. Arrange professional diagnosis to identify whether the fault involves the PCB, wiring, capacitor, compressor, or another component.
10. Incorrect Aircon Capacity
An aircon that is too small for the room may operate continuously without reaching the desired temperature.
Cooling demand is affected by:
- Room floor area
- Ceiling height
- Number of occupants
- Direct sunlight
- Window size
- Heat-producing equipment
- Room usage
- Door-opening frequency
- Insulation
- Required operating hours
If the aircon has never cooled the room properly—even when new and clean—the installed capacity may be insufficient.
Arrange a site assessment before replacing the unit. Letscool Aircon provides aircon installation services in Singapore for HDB flats, condominiums, landed homes, and commercial premises.
Why Is My Aircon Running but Not Cooling?
An aircon running but not cooling usually means the indoor fan is operating while the refrigeration or heat-rejection process is not working correctly.
Possible causes include:
- Fan Mode selected instead of Cool Mode
- Dirty evaporator coil
- Refrigerant leakage
- Outdoor unit not operating
- Faulty compressor
- PCB communication fault
- Temperature-sensor problem
First, select Cool Mode and wait 15–20 minutes. If the outdoor unit does not start or the air remains warm, arrange an inspection.
Why Is the Aircon Blowing Air but Not Cold?
When an aircon blows air but it is not cold, the indoor fan is working, but the air may not be passing across a properly cooled evaporator coil.
Check the remote settings and washable filter first. If these are correct, the system may have a dirty coil, frozen coil, refrigerant problem or outdoor-unit fault.
Do not assume that every case requires a gas top-up. Gas pressure should be checked together with the overall system condition.
Why Is One Aircon Unit Not Cold but the Others Are?
If only one indoor unit in a multi-split system is not cold, the problem is more likely to be associated with that indoor unit or its refrigerant-control circuit.
Possible causes include:
- Dirty filter or blower
- Faulty thermistor
- Fan motor problem
- Expansion-control problem
- Communication fault
- Refrigerant distribution issue
- Incorrect settings for that unit
Compare the airflow and temperature with the other indoor units. A technician should inspect the affected fan coil and review any error codes.
Why Is My Aircon Cold at Night but Not During the Day?
An aircon that cools at night but struggles during the day may be affected by a higher daytime heat load.
Common reasons include:
- Direct afternoon sunlight
- Large windows
- Poor curtains or blinds
- Warm air entering through open doors
- Top-floor heat
- High occupancy
- Heat-generating equipment
- Insufficient aircon capacity
- Dirty outdoor condenser
- Outdoor unit overheating
Close doors and windows, reduce direct sunlight, and confirm that the unit is correctly sized. If the system previously cooled well during the day but no longer does, servicing or repair may be required.
Why Is My Aircon Not Cold After Servicing?
Aircon servicing removes dirt and improves airflow, but it cannot automatically repair every mechanical, electrical, or refrigerant fault.
If the aircon remains warm after servicing, possible causes include:
- Refrigerant leakage
- Faulty sensor
- Fan motor problem
- Compressor fault
- PCB problem
- Incorrect diagnosis
- Outdoor-unit issue
- Insufficient system capacity
Contact the servicing company and explain when the problem started. Ask for operating-temperature checks and proper diagnosis rather than requesting an automatic gas top-up.
Does an Aircon That Is Not Cold Need Gas Top-Up?
Not necessarily. Dirty filters, incorrect settings, weak airflow, sensor faults, fan problems, and compressor issues can all cause poor cooling without low refrigerant.
Aircon gas top-up is appropriate only after a technician confirms that the refrigerant charge is insufficient and investigates why.
If cooling improves for only a short period after every top-up, the system may have an unresolved refrigerant leak.
General Service vs Chemical Wash vs Aircon Repair
| Service | Suitable when | Not intended to fix |
|---|---|---|
| General service | Filters and components have light dirt; airflow needs maintenance | Refrigerant leaks, PCB faults or failed motors |
| Chemical wash | Coil, blower or drainage system has heavier contamination | Compressor, sensor or electrical failure |
| Chemical overhaul | Indoor fan coil requires deeper dismantling and cleaning | Incorrect sizing or major outdoor-unit faults |
| Gas top-up | Testing confirms insufficient refrigerant | Dirty filters or unrelated electrical problems |
| Aircon repair | A component, connection or control has failed | Normal maintenance cleaning |
The correct service should be selected after diagnosis. Paying for repeated cleaning will not solve a faulty component, while replacing parts will not solve a simple dirty-filter problem.
How Much Does Aircon Repair Cost in Singapore?
Aircon repair costs in Singapore depend on the fault, brand, model, unit type, accessibility, and parts required.
A filter or basic maintenance problem usually costs less than refrigerant leak detection, fan-motor replacement, PCB repair, or compressor work.
Before approving a repair, ask for:
- Diagnosis of the actual fault
- Scope of repair
- Labour charges
- Parts cost
- Applicable warranty
- Additional testing required
- Whether the quotation includes GST
Avoid approving a gas top-up without asking why the refrigerant level is low.
When Should You Call an Aircon Technician?
Arrange professional inspection when:
- The aircon remains warm after basic checks
- Ice repeatedly forms
- The outdoor unit does not start
- Airflow remains weak after filter cleaning
- The circuit breaker trips
- The aircon displays an error code
- A burning smell or unusual noise appears
- Water leakage accompanies weak cooling
- Cooling returns only briefly after gas top-up
- More than one indoor unit stops cooling
- The system is old and breaks down repeatedly
Switch off the unit immediately if it repeatedly trips the circuit breaker, produces a burning smell, or has water near electrical components.
Why Choose Letscool Aircon?
Letscool Aircon provides aircon servicing, inspection, and repair for HDB flats, condominiums, landed properties, offices, and commercial premises across Singapore.
Our technicians can inspect:
- Remote and operating settings
- Air filters
- Evaporator coil and blower
- Indoor and outdoor fan motors
- Drainage system
- Thermistors and sensors
- PCB communication
- Refrigerant pressure and leakage
- Outdoor condenser condition
- Compressor operation
For help with an aircon not cold or not cooling properly, call or WhatsApp Letscool Aircon at +65 9862 3678.
Frequently Asked Questions
Why is my aircon running but not cooling?
An aircon running but not cooling may have incorrect settings, a dirty filter or coil, low refrigerant caused by leakage, a frozen evaporator coil, or an outdoor-unit fault. Check Cool Mode and the filter first. If the air remains warm, arrange a professional inspection.
Why is my aircon blowing air but not cold?
The indoor fan may be operating while the evaporator coil is not cooling properly. Possible causes include Fan Mode, a dirty coil, refrigerant leakage, a frozen coil, compressor trouble, or an outdoor-unit problem.
Can a dirty filter cause the aircon not to be cold?
Yes. A dirty air filter restricts airflow through the evaporator coil. This reduces the volume of cooled air entering the room and may also contribute to coil freezing.
Does an aircon that is not cold need gas top-up?
Not always. Incorrect settings, dirty components, weak airflow, sensor faults, fan problems, and compressor issues can also cause poor cooling. A technician should confirm the refrigerant condition and check for leakage before adding gas.
Why is only one aircon unit not cold?
If only one indoor unit is not cold, the problem may involve its filter, blower, fan motor, sensor, expansion control, or refrigerant distribution. The affected indoor unit should be inspected separately.
Why are all my aircon units not cooling?
If every indoor unit connected to the same system is not cooling, the problem may involve the outdoor unit, compressor, refrigerant circuit, power supply, PCB communication, or system controls.
Why is my aircon cold at night but not during the day?
Daytime sunlight, high outdoor temperature, open doors, large windows, or insufficient aircon capacity may increase the room’s heat load. A dirty outdoor condenser or a weakening system can also make daytime cooling worse.
Why is my aircon not cold after servicing?
Servicing may clean the filters and fan coil but cannot repair every mechanical, electrical, or refrigerant fault. The system may still have a gas leak, faulty sensor, fan motor problem, PCB fault, or compressor issue.
Can I fix an aircon cooling problem myself?
You can check Cool Mode, replace remote batteries, clean washable filters, close doors and remove airflow obstructions. Refrigerant, electrical, PCB, fan-motor, and compressor repairs should be handled by a trained technician.
How much does aircon not-cold repair cost in Singapore?
The cost depends on the diagnosis, brand, model, accessibility, labour, and replacement parts required. Basic servicing generally costs less than refrigerant leak repair, fan-motor replacement, PCB work, or compressor repair. Obtain a written quotation after inspection.