Why is my aircon not cold?
When your aircon runs but the room stays warm, blocked airflow, a refrigerant leak, a compressor fault, and a room outpacing the unit all look identical from the doorway. The fastest way to separate them is airflow strength, outdoor-unit behavior, and how cooling fades with time.
By Team Snowflake | Reviewed 30 May 2026
1. Blocked airflow
You feel less wind at the outlet, and what does come through barely cools. The unit is still running, but a clogged filter, dirty blower, or dust-loaded coil means less room air is crossing the coil each minute, so less heat gets carried away.
How to tell
Start your hand at the outlet. With blocked airflow the wind itself feels weaker, thin and lazy rather than strong. That is the giveaway: unlike a refrigerant leak, where airflow stays strong but the air stops feeling cold, here the volume is down. The outdoor unit still cycles normally, unlike a compressor fault. The decline builds slowly over weeks.
- Wind at the outlet feels weaker and thinner than it used to.
- Cooling is uneven, stronger near the unit and warm across the room.
- It has been getting gradually worse over weeks, not all at once.
How we confirm it
We check the filter, blower wheel, and indoor coil for restriction first. When one of them is loaded with dust, clearing it restores the airflow volume and cooling usually returns the same visit.
Never agree to a gas top-up before the filter has been opened and checked. Weak airflow and low refrigerant feel identical from the room, but airflow is the cheaper check and the more common cause. Paying for gas first means paying twice when the real problem was a dirty filter.
2. Refrigerant leak
Airflow feels normal, a healthy push of air at the outlet, but that air is no longer properly cold. The system is moving plenty of room air across the coil while carrying too little refrigerant to pull the heat out of it, so the room cools more slowly than it should.
How to tell
The signature is strong wind with weak cold. Hold your hand at the outlet: the volume of air feels normal, unlike blocked airflow where the wind itself thins out. The fade is slow over weeks, not a sudden stop in a day, which separates it from a compressor fault.
- Wind at the outlet still feels strong, but the air is not properly cold.
- Cooling was fine before and has faded steadily over weeks.
- The room takes much longer than usual to reach a comfortable temperature.
How we confirm it
We pressure-test the system, trace the leak point, seal it, then recharge to the correct level. A recharge only happens after the leak is found and repaired, never before.
Never settle for repeated top-ups, because that treats the symptom and not the fault. Adding gas before the leak is found lets the refrigerant keep escaping, so the warm room returns within weeks and you pay for the same fault again. The leak has to be sealed once for the cooling to hold.
3. Compressor or start fault
Air keeps blowing from the indoor unit, but it is close to room temperature. The indoor fan runs on its own circuit, so it carries on even when the compressor outside never starts properly, which means the refrigerant is not actually being pumped and almost no heat is being removed.
How to tell
Walk to the outdoor unit and listen. A healthy unit settles into a steady hum. A failing capacitor often buzzes or clicks as the compressor strains to start, and a dead one may sit silent. Unlike a refrigerant leak, where the outdoor unit runs normally and cooling fades slowly, here the room went warm in a day.
- Indoor air blows steadily but feels close to room temperature.
- Outdoor unit sounds wrong: silent, buzzing, or clicking and stopping.
- Cooling dropped off suddenly, and longer runtime changes nothing.
How we confirm it
We test the capacitor and contactor at the outdoor unit and measure the compressor's current draw. A weak capacitor or contactor is a small replacement; the compressor itself is only confirmed faulty when the readings rule everything else out.
Do not let anyone condemn the compressor before the capacitor and contactor are tested. A failed capacitor produces the exact same symptom and is one of the lowest-cost parts on the unit, while a compressor swap is the single most expensive repair in the system. Testing before replacing is what keeps a minor job from being quoted as a major one.
4. Room heat load exceeds unit capacity
The outlet still blows genuinely cold, yet the room never quite cools down. The unit is working, but the room gains heat faster than the aircon can remove it. This is common where afternoon sun, large glass, or thin insulation lets heat in faster than the installed capacity can keep up.
How to tell
Watch the clock, because this fault follows the sun. The shortfall is worst in the hot afternoon, eases at sunset, and fades on cloudy days. Unlike a refrigerant leak or a compressor fault, it comes and goes with the weather. The outlet still feels cold to your hand throughout, not weak as with blocked airflow.
- Cooling falls behind through the hot afternoon and recovers after sunset.
- Other rooms on the same system cool down normally.
- The outlet still blows cold even while the room stays warm.
How we confirm it
We compare the outlet air temperature against the room temperature. When the unit output is within range, the answer sits on the room side, shading, insulation, or matched capacity, rather than anything inside the aircon.
When the room stays warm in the afternoon heat, the instinct is to ask for a gas top-up, and that is the wrong call here. A unit cooling within range gains nothing from added refrigerant, so the gas spend solves nothing while the room keeps overheating. The fix is reducing the heat load or matching capacity to the room, not touching the refrigerant.
Useful next steps
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