An AC not cooling is usually caused by a dirty filter, dirty coils, low refrigerant, a faulty capacitor or compressor, a frozen coil, wrong settings, a sensor fault or a unit that is too small for the room. Check the remote, filter and outdoor unit first. If cooling does not return, switch the AC off and call a technician, because gas and electrical faults are not DIY jobs.
It’s a hot afternoon in Colombo. The AC is running, you can hear the fan, but the room just isn’t getting any cooler. Sound familiar?
Most cooling problems come down to a handful of common causes, and a few you can check yourself in five minutes. Below are eight of them, what each looks like and what usually fixes it, plus which jobs need a technician.
We see these faults every day across Colombo and the nearby suburbs, so this comes from what we actually find on site. If you’d rather skip the reading, our house AC repair team can come and look.
Why is my AC running but not cooling?
Most often it is restricted airflow from a dirty filter or coil, low refrigerant caused by a leak, or a failing part such as the capacitor or compressor. Less often it is a settings mistake, a frozen coil, a sensor fault or a unit that is too small for the room. The table matches what you notice to the likely cause.
| What you notice | Likely cause | Who fixes it |
|---|---|---|
| Weak airflow, dusty smell | Dirty filter | You |
| Cool, not cold, and runs for hours | Dirty coils | Technician |
| Cooling fades over weeks, ice on pipes | Low refrigerant | Technician |
| Outdoor fan or compressor silent | Faulty capacitor or compressor | Technician |
| Ice on the indoor unit | Frozen coil | Switch off, then technician |
| Unit on, room still warm | Wrong mode or temperature | You |
| Blinking light or error code | Sensor or PCB fault | Technician |
| Runs all day, never catches up | Unit too small | Technician advice |
A quick AC not cooling fix checklist
Before anything else, try these five checks. They solve more than you’d expect.
- Check the remote. Set the mode to Cool (not Fan or Dry), the temperature below room temperature, and put in fresh batteries.
- Look at the filter. Slide it out. If you can’t see light through it, wash it gently, dry it fully and refit it.
- Check the outdoor unit. The fan should be spinning and the area around it clear of leaves, boxes and clutter.
- Look for ice. Ice on the indoor unit or the copper pipe means you should switch the AC off and let it melt.
- Wait fifteen minutes. Close doors and windows, then see if the room starts to cool.
If nothing here helps, the cause is probably inside the system.
The 8 causes, one by one
1. A dirty air filter
Dust and pet hair clog the mesh and choke the airflow. The unit keeps running, but little cool air reaches the room. The U.S. Department of Energy calls cleaning or replacing filters a critical maintenance task, and says units that run constantly or sit in dusty spots need checking more often.
Fix: wash it about once a month, and let it dry fully before refitting.
2. Dirty indoor or outdoor coils
The coils move heat out of your room. Once they’re coated in grime, they can’t do it well, so the AC runs longer and cools less. Outdoor coils clog quickly near busy roads and building sites, and salty coastal air can wear them down.
Fix: a proper aircon servicing visit washes the indoor coil, blower wheel and drain line.
3. Low refrigerant or a gas leak
Refrigerant (gas) carries heat out of your room. It isn’t used up like fuel, so low gas almost always means a leak. Typical signs are cooling that fades over weeks, ice on the pipes and a hissing sound. Topping up without finding the leak only buys a few weeks.
Fix: a technician leak-tests first, repairs it, then recharges (R22, R32 or R410A). This is never a DIY job.
4. A faulty capacitor or failing compressor
The capacitor gives the compressor and fan motors the kick they need to start. When it weakens, the outdoor fan may hum, click or refuse to turn while the indoor unit keeps blowing air. A failing compressor is the more serious fault.
Fix: a technician can test both and, for a capacitor, usually replace it in the same visit. Please don’t open the outdoor unit yourself.
5. A frozen evaporator coil
If there’s ice on the indoor unit or the pipe, the coil has frozen. This usually comes from restricted airflow or low refrigerant, and This Old House notes that a leak can freeze the coil too.
Fix: switch the AC off, let the ice melt fully, then clean the filter. If the ice comes back, call a technician.
6. Wrong settings or a tired remote
It happens more than people admit. The mode may be on Fan, Dry or Auto, the temperature set too high, or a sleep timer may have switched the unit off. Flat remote batteries can cause it too.
Fix: set Cool mode, lower the temperature and clear any timers. Also shut doors and windows and draw curtains against afternoon sun.
7. Error codes, sensor or PCB faults
Inverter units depend on sensors and a control board (PCB). A faulty sensor can fool the unit into thinking the room is already cool, and a blinking light or error code usually points to the problem. Codes differ between LG, Samsung, Daikin, Midea and others.
Fix: photograph the code and send it to a technician. These are specialist air conditioner repair jobs, often fixed at board level.
8. A unit that is too small for the room
An AC sized for a small bedroom will struggle in a bigger room, a west-facing room that heats up in the afternoon, or a space that now holds extra people or equipment. It runs non-stop and never quite catches up.
Fix: cut the heat load with curtains and good sealing, and ask a technician about the right capacity before you replace anything.
Can I fix an AC that is not cooling myself?
Yes for the simple causes: settings, the filter and clearing space around the outdoor unit. No for anything involving gas, electrics or the compressor, where a wrong move can cost more than the repair itself.
- Safe to try: cleaning the filter, resetting the remote, clearing leaves from around the outdoor unit and letting ice melt with the AC switched off.
- Leave to a technician: gas refills, leak repairs, capacitors, compressors, circuit boards and anything inside the outdoor unit.
How do you keep an AC cooling properly?
Wash the filter monthly, keep the outdoor unit clear and book a professional air conditioning service once or twice a year.
Regular aircon servicing also lets a technician spot a weak capacitor or a slow leak before it leaves you without cooling in the hottest week. You can see everything we offer, from house calls to office and industrial work, on our AC repair and service page.
When should you call a technician?
Call a technician if the AC still isn’t cooling after the basic checks, or sooner if you notice any of these:
- Ice that keeps coming back
- A hissing sound, clicking or a burning smell
- An outdoor fan or compressor that won’t start
- The breaker tripping when you switch on
- An error code or blinking light
Here’s what happens when you book with Orient:
- A technician usually reaches most Colombo homes in 2-4 hours, and a message before noon can mean a same-day repair.
- The inspection fee is confirmed when you book and comes off the bill if you go ahead.
- We agree the repair price with you on WhatsApp before anything is opened.
- Every repair carries a 3-month workmanship warranty, and we use genuine spares.
Looking for affordable AC repair in Colombo?
Affordable doesn’t have to mean the cheapest quote. It means knowing the cost before you commit. We don’t publish a price list, because a capacitor and a compressor are very different jobs, but we do promise the order things happen in: diagnosis first, price second, repair last.
Our customers say it best:
Excellent service! They arrived on time, diagnosed the AC issue quickly, and fixed it without any hassle.
S H Jayamal, Google review
Need AC repair and service in Colombo?
Send a photo of the unit on WhatsApp and tell us what it is doing. We’ll come back with a likely cause, a price and a time slot. Whether you need AC service Colombo-wide or in the southern suburbs, we’re open 8.00am-8.00pm, seven days a week, including poya days.
You can also call 070 633 5435 or contact Orient Air Conditioning for directions to our Pannipitiya base.
Frequently asked questions
Why is my AC blowing warm air?
Warm air usually means the outdoor unit isn’t getting rid of heat. The usual causes are low refrigerant, a dirty condenser coil or a faulty capacitor or compressor, though a remote set to Fan or Dry mode is also common. Check the mode and the outdoor fan first, then call a technician if the air stays warm.
Can low gas stop an AC from cooling?
Yes. With less refrigerant in the system, the AC removes less heat, so cooling fades. Gas isn’t used up, so low gas points to a leak. A good technician finds and fixes the leak before recharging, otherwise the problem returns within weeks.
How often should I service my AC in Colombo?
Once or twice a year suits most homes, and every few months for units that run all day in a dusty room. Wash the filter yourself about once a month in between, and book a technician if cooling starts to fade.
How long does a full AC service take?
A full air conditioning service on a single split unit usually takes an hour to ninety minutes. It covers the indoor coil, blower wheel and drain line, and we cover furniture and protect the floor first.
How fast can Orient reach me for a repair in Colombo?
Most Colombo homes are reached in 2-4 hours, and a message before noon can often mean a same-day repair. We’re open 8.00am-8.00pm, seven days a week, including weekends and poya days.