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Why Is My Aircon Not Cold? Fixes and Costs (2026)

Prices checked October 2026 against the published price lists of 526 contractors listed on Homees, MOM's 2025 wage data and Qanvast's 2026 report. How we price →

An aircon that runs but doesn't cool has a short list of usual suspects. Here's how to narrow it down — what you can check yourself, what needs a technician, and what each fix should cost in Singapore.

Quick answer: The most common causes are a dirty filter, low refrigerant gas, or a clogged condenser — often fixed with a S$60–S$150 servicing or gas top-up. Compressor and coil faults cost more. If a basic clean and gas check doesn't restore cooling, engage a technician before the problem worsens.

Key takeaways

A clogged filter or coils is the most common — and cheapest — cause; regular servicing prevents most of it.
Weak cooling that returns after a gas top-up points to a refrigerant leak that needs sealing, not just refilling.
Compressor, thermostat and fan-motor faults need a professional diagnosis.
An undersized unit will never cool a large room — that's a BTU sizing issue, not a fault.

What to do first when your aircon stops blowing cold

Work from cheapest to most involved: check the filter and temperature setting, confirm the outdoor unit is running, then look at gas pressure and coils. Most cases are resolved at the servicing stage; the list below covers every likely cause so you know what your technician is talking about.

Dirty or clogged air filter

The air filter traps dust and airborne particles before they circulate into the room. When it clogs with grime, airflow drops, the evaporator coil can freeze over, and cooling efficiency falls. The unit then works harder while cooling the room less.

Cleaning the filters every few weeks solves most of this. On top of that, book general servicing regularly and a chemical wash or overhaul roughly every six to twelve months — a chemical wash lifts stubborn residue that general servicing cannot.

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Faulty compressor

The compressor is the heart of the system — it pressurises the refrigerant that cools the air. If it's failing or blocked by dirt and debris, the unit can blow warm air instead of cold. This is a professional job: a technician will diagnose whether it can be repaired or needs replacing. See our full guide to aircon compressors.

Clogged condenser coils

The condenser coils (in the outdoor unit) expel the heat drawn from your room. Caked in dust, they can't shed heat efficiently, so the system struggles to cool. Regular servicing clears them; a chemical overhaul is the deeper fix for heavy build-up.

Low gas pressure

If refrigerant pressure drops below normal, cooling weakens noticeably. Gas escapes through cracked pipes, poor installation joints, or corrosion in the internal unit. The fix is to locate and seal the leak first, then top up the gas — refilling without sealing just buys a few weeks before you're back to warm air. See typical gas top-up rates.

Coolant or refrigerant leaking

The refrigerant is the fluid the compressor circulates to cool the air. A leak reduces the compressor's efficiency and, in turn, the cold air reaching the room. As above, the fix is to identify the leak source, repair or replace the affected part, then replenish the refrigerant.

Faulty thermostat

The thermostat reads room temperature and tells the system when to cool. If it misreads the temperature or fails to trigger the compressor, every other component can be working perfectly and the room still won't cool. Replacing a faulty thermostat resolves it.

Leaking evaporator coils

The evaporator coils (in the indoor unit) absorb heat from the room and pass it to the condenser, circulating refrigerant as they go. Dust build-up cuts their efficiency; a leak lets refrigerant escape and reduces cooling further. A half-yearly clean is a good baseline. If you also have an aircon leaking water problem, the two issues are often related — a technician can diagnose both.

Clogged drain pipes

Drain pipes carry away the moisture the unit pulls from the air. When mould and dirt block them, water can't drain, efficiency drops, and the unit works harder to hold temperature. Flushing the drain pipes restores normal drainage — and usually the cooling with it.

Ductwork or insulation issues

If your cool air is distributed through ducting, any blockage or leak in the ducts lets cold air escape before it reaches the room. The same happens when rooms, windows or doors are poorly sealed — cool air leaks out and the unit can't keep up. Sealing gaps and, where relevant, adding window solar film both help the system hold temperature.

Faulty fan motor

If the indoor or outdoor fan motor fails, the unit can't move enough air to cool the room. Tell-tale signs are a buzzing noise and warm output, and the cause is often an electrical fault in the wiring. This needs a trained technician to examine and repair. As a rough guide, repairing a single fan coil unit runs about S$35–S$120 depending on the fault; see the full aircon cost guide.

What it costs to fix

Issue	Typical fix	Indicative cost
Dirty filter / light clog	General servicing	S$30 – S$60 per unit
Heavy coil build-up	Chemical wash / overhaul	S$80 – S$250 per unit
Low gas	Leak check + gas top-up	S$60 – S$150
Faulty thermostat	Replace thermostat	S$80 – S$200
Fan motor fault	Repair / replace	S$35 – S$150
Compressor fault	Repair or replace	S$200 – S$900+

Indicative 2026 ranges; final cost depends on brand, unit age and access. Always get the price confirmed before work starts.

What's the best temperature for cooling in Singapore?

Given Singapore's tropical climate, 24–25°C is widely recommended as the most energy-efficient setting that still cools comfortably. Around 16–18°C feels cold quickly but is rarely ideal for sleep — for rest, most guidance points to 24–26°C. To reduce how hard your aircon has to work, solar film on sun-facing windows cuts incoming heat and UV.

Is my aircon the right size for the room?

If cooling is weak everywhere and the unit is otherwise healthy, it may simply be too small for the space. An undersized system can't cool a large room no matter how long it runs — the fix is a higher-BTU unit matched to the room. Our BTU sizing guide shows how to match capacity to room size.

Should I turn off my aircon if it isn't cooling?

Yes. If the unit isn't cooling, switch it off and let it rest for a few hours rather than running it non-stop — continuous strain on a struggling unit can cause a frozen coil or a blown capacitor. Turn it off when it's not in use, and book a technician if resting and a basic clean don't restore cooling.

Which aircon mode cools best?

Cool mode — fan runs continuously, compressor cycles to hold your set temperature. Best for steady cooling.
Fan mode — fan only, compressor off. Ventilation without cooling.
Dry mode — reduces humidity rather than temperature; useful on damp days.
Energy saver mode — compressor and fan cycle on and off to limit power use.
Sleep mode — works with cool mode, gradually easing the temperature up overnight for comfort.
Fan speed (low/medium/high) — affects airflow, not cooling capacity.
Timer-off — schedules the unit to switch off automatically.

FAQ

Why is my aircon running but not cold? The usual causes are a dirty filter, low refrigerant gas, or clogged condenser coils. Start with servicing and a gas check — if cooling doesn't return, have a technician check the compressor, thermostat and fan motor.

How much does it cost to fix an aircon that isn't cooling? Simple fixes like servicing or a gas top-up run S$30–S$150. Thermostat or fan-motor repairs are S$35–S$200, while a compressor repair or replacement can be S$200–S$900+.

Can I fix an aircon that's not cold myself? You can clean the filters and check the temperature setting and outdoor unit. Anything involving refrigerant, the compressor, coils or electrical wiring should be left to a trained technician.

Why does my aircon only cool for a while then turn warm again? That pattern usually means a refrigerant leak — the gas is escaping faster than it should. It needs the leak sealed before topping up, not just a refill.

What temperature should I set my aircon in Singapore? Around 24–25°C is the sweet spot for efficient cooling, and 24–26°C for comfortable sleep. Lower settings cost more to run without much added comfort.

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