The AC runs but doesn't cool — causes and fix
Before you pay a call-out fee: more than half of all 'my AC won't cool' cases are solved by cleaning. Work through these steps in order. If they don't fix it, you'll at least know it's a refrigerant or compressor problem — and that is a technician's job.
The problem
The fan runs and air comes out, but it isn't cold — or it's barely cool. Sometimes it cools at first and then fades, or the indoor unit drips water, or there's ice on the copper pipes, or the outdoor unit runs but no hot air comes off it.
Likely causes
A dust-clogged filter (the number one cause, by a mile)
The filter is there to catch dust — and once it's saturated, it stops air reaching the cold coil. The result: weak airflow, weak cooling, and sometimes a frozen coil. In a hot, dusty climate that means cleaning it monthly in summer, not yearly.
A dirty or boxed-in outdoor unit (the condenser)
The outdoor unit's whole job is to dump heat outside. If its fins are packed with dust and lint, or boxes and laundry are stacked against it, or it's in direct sun with no airflow, it can't dump that heat — so cooling collapses even with a full gas charge.
The indoor coil is frozen over
If you see white ice on the copper or the coil, switch the AC off and run the fan only for an hour to let it thaw. Freezing is a symptom, not a cause — it comes from either low airflow (filter) or low refrigerant. If it re-freezes after you've cleaned the filter, it's refrigerant → technician.
Low refrigerant because of a leak
An AC is not a car — it doesn't consume refrigerant. If it's low, there's a leak. Anyone who offers to top it up without finding the leak is selling you the same problem again in a few months. Finding it needs a leak detector and a vacuum pump — technician only.
A failed capacitor or compressor
If the outdoor fan spins but you hear no compressor, or it clicks and cuts out, it's usually the capacitor. It's a relatively cheap part — but replacing it means working with mains power and a component that stores a charge → technician.
The remote settings
It sounds silly, and it happens constantly: the unit is on Fan or Dry instead of Cool, or the setpoint is 28°C, or Eco mode is on. Check this before you take anything apart.
Fix it — step by step
- Check it's actually set to coolTake the remote and confirm the mode is Cool (the snowflake), not Fan or Dry, that the setpoint is 22-24°C, and the fan is on High. Turn Eco / Energy Saving off for now.If it's on Fan, it is literally a fan — it will not cool by a single degree, and nothing is broken.
- Cut the powerAt the AC's breaker in the panel, not just with the remote. Everything from here on happens with the unit dead.If you can't identify the breaker, kill the main. Better than a guess.
- Take the filters outLift the front cover of the indoor unit (it usually swings up by hand, no tools). Inside are one or two mesh filters. Slide them out gently.Photograph them with your phone before you remove them so they go back the right way round.
- Wash them in warm soapy waterRinse from the clean side so the dust is pushed back out, scrub with a soft brush and dish soap, then let them dry completely in the shade. Don't refit them wet and don't blast them with a hairdryer.If a filter is torn or has gone stiff like cardboard, replace it — cleaning won't bring it back.
- Gently clean the indoor coilBehind the filter is a coil of thin aluminium fins. Run a soft brush or a vacuum brush attachment along them, in the same direction as the fins. Don't press hard and don't bend them.If there's ice, don't chip it off — let it melt.
- Go outside and clean the condenserClear everything stacked around it — boxes, plants, laundry — and leave at least half a metre of clearance on every side. Rinse the fins with a normal garden hose, top to bottom. Not a pressure washer.High pressure bends the fins flat and makes the unit worse, not better. Ordinary water is enough.
- Check the drain isn't blockedThe hose running out of the indoor unit must be clear. If water is dripping from the unit down the wall, the drain is usually clogged. A puff of air or a flexible wire clears it.Water coming off an AC is normal — it just has to leave through the hose, not the wall.
- Power up and run it for an hourRefit the dry filters, close the cover, turn the breaker back on, and run it on Cool at 22°C with the fan on high. Give it a full hour before you judge it.Use a thermometer, or just your hand: the air coming out should be clearly colder than the room.
- If it still won't cool — make the callIf the filters are clean, the outdoor unit is clean, and the air still isn't cold — or the coil freezes again — it's refrigerant, capacitor or compressor. Stop here and call an AC technician.Tell them exactly what you already did. It saves you the diagnostic fee and sends them straight to the real cause.
Tools & parts you'll need
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When to call a professional
Call an AC technician if: the coil freezes again after you've cleaned the filters; the outdoor unit won't start at all, or clicks and cuts out; there's oil or a greasy film on the copper joints (a refrigerant-leak tell); or the breaker trips every time the AC starts. And never try to charge refrigerant or open the cooling circuit yourself — it's under high pressure and will give you an instant freeze burn.
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Try photo diagnosisPeople also ask
How often should I clean the AC filter?
In summer, in a hot and dusty climate, with daily use: every 2-4 weeks. In cooler weather or with light use: every couple of months. A clean filter also cuts your bill — an AC with a clogged filter has to run longer to reach the same temperature.
Doesn't an AC need a gas top-up every year?
No — this is the biggest myth in the trade. An AC is a sealed loop; it doesn't burn refrigerant the way a car burns fuel. If it's low, there is a leak. A good technician finds and fixes the leak before recharging it.
Why is ice forming on the AC pipes?
Ice forms when too little air passes over the cold coil (clogged filter, weak fan) or when pressure is low because refrigerant is short. Switch it off, run the fan only until it thaws, then clean the filter. If it freezes again — it's refrigerant.
It cools fine but my electricity bill has exploded
Check: clogged filter, outdoor unit sitting in direct sun with no shade, doors and windows leaking air, and a setpoint below 22°C. Every degree below 24°C costs roughly 5-8% more power. 24°C plus a ceiling fan feels colder than 20°C on its own.
The indoor unit is dripping water down the wall
Almost certainly the drain hose is blocked with dust and algae, so the internal tray overflows. Clearing the hose fixes it. If the hose is clear and it still drips, the unit may have been mounted at the wrong tilt.
Can I clean the outdoor unit with a pressure washer?
Better not to. High pressure flattens the thin aluminium fins and reduces the unit's ability to shed heat — so you make the problem worse. A normal hose, top to bottom, is the right tool.