Aircon Not Cooling? When to Call a Technician (7 Causes)

Why your aircon runs but the room stays warm

An aircon that is not cooling properly is one of the most frustrating problems in a hot Kariega summer. The unit is on, the fan is blowing, yet the room stays warm. The good news is that most causes fall into a handful of familiar categories, and a few of them you can fix yourself in minutes — while others need a registered technician.

The causes below run from the simplest and most common to the most serious. Work through them in order, and stop at the point where the job needs a professional: refrigerant, electrical and compressor work is not a DIY project.

Seven common causes, from simplest to most serious

1. A dirty or blocked air filter. This is the number one cause of weak cooling. A clogged filter chokes the airflow across the indoor coil, so the room never gets properly cold. Take the filter out, wash it with warm water and mild soap, dry it fully and refit it. Do this every few weeks during summer.

2. Wrong settings on the remote or thermostat. Check that the unit is on cool mode, not fan-only, and that the set temperature is actually below the room temperature. A unit set two degrees above the room will simply circulate air.

3. Doors and windows open, or heat sources close by. Every open door and window lets the cold air out and warm air in, and the unit will run forever without catching up. Close the room up while the aircon runs.

4. A blocked or dirty outdoor unit. The outdoor condenser needs to dump heat outside. If it is buried under leaves, against a wall, or caked in dust, the system cannot reject heat and cooling collapses. Clear at least half a metre of space around it and hose the fins down gently.

5. Ice forming on the indoor coil or pipes. Ice usually means poor airflow or a low refrigerant charge. Switch the unit off, let it defrost, then check the filter. If the ice returns, it is a refrigerant problem and needs a technician.

6. Low refrigerant (gas) or a leak. If the air is lukewarm rather than cold, and the unit runs constantly, the system may be low on gas. Low gas always means a leak somewhere — topping it up without finding and fixing the leak is money thrown away. This must be done by a SAQCC-registered technician.

7. A failing capacitor, fan motor or compressor. If the outdoor fan is not spinning, the unit trips the breaker, or you hear grinding or buzzing, a component is failing. Running the unit like this can turn a small repair into a full replacement.

Check these yourself before you call

Before you spend money on a call-out, run this five-minute checklist: clean or check the air filter, confirm the remote is on cool mode with a sensible set temperature, close the doors and windows, clear anything blocking the outdoor unit, and switch the unit off for ten minutes to let any ice melt and the system reset.

That genuinely fixes a large share of 'aircon not cooling' calls. If the unit still blows warm air, the filter is clean and the outdoor unit is clear, the problem is almost certainly refrigerant, electrical or mechanical — which is where a professional comes in.

When it is time to call a professional

If your checks do not solve it, or you notice any of the signs in our guide to air conditioning repairs — a tripping breaker, strange noises, water inside, or a burning smell — stop using the unit and call a technician. Running a struggling compressor is the fastest way to turn a repairable fault into a full replacement.

A registered technician will measure the refrigerant pressures, find and repair any leak, check the electricals and test the airflow. After load shedding in particular, a surge can damage the capacitor or circuit board — the surge when the power returns is one of the most common causes of failure in this region, so if your aircon stopped cooling right after an outage, say so when you call.

Weak airflow or warm air? How to tell them apart

The two most common complaints — weak airflow and warm air — point to different problems, and telling them apart narrows the diagnosis. Weak airflow means the fan is struggling: a blocked filter, a dirty indoor coil or a failing fan motor. Warm air at full fan speed usually means the cooling side has failed: low refrigerant, a stuck expansion valve or a compressor problem.

A simple test helps. Set the fan to high and hold your hand in front of the indoor unit. If the air moves strongly but is not cold, suspect the refrigerant or compressor. If the air barely moves, check the filter first — then suspect the fan or coil. Either way, if the filter is clean and the unit still underperforms after your own checks, the next step is a professional diagnosis.

One more common cause in South African homes: the unit may be too small for the room, or the room may have grown hotter — new windows facing the sun, a tin roof, or an open-plan renovation all add heat load. If the aircon never quite kept up since day one, sizing is the real problem, and our BTU sizing guide explains how to match a unit to a room.

Do not keep running a struggling unit

It is tempting to leave the unit on and hope it cools down, but a system that is low on gas or running with a failing component works harder every hour it runs. Low refrigerant makes the compressor run hot, which shortens its life; an electrical fault can trip breakers or, in a bad case, damage the circuit board. The repair bill only grows the longer the fault runs.

If the unit is blowing warm air, switch it off and book a diagnosis. A technician will pressure-test the system, find the leak or the failing part, and give you a written quote before starting work — so a check costs you little, but a burned-out compressor costs you a lot.

Frequently asked questions about aircon not cooling

Q: Why is my aircon running but not cooling?

A: The most common causes are a dirty air filter, the wrong settings, a blocked outdoor unit, or low refrigerant. Work through the checklist above before calling.

Q: Why is my aircon blowing warm air?

A: Warm air usually points to low refrigerant, a compressor problem, or the unit running in fan-only mode. If the filter is clean and the settings are right, call a technician.

Q: Why is ice forming on my aircon pipes?

A: Ice means poor airflow or low gas. Switch the unit off and let it defrost, check the filter, and if the ice returns, book a service — low gas is a leak.

Q: Can I add aircon gas myself?

A: No. Refrigerant handling in South Africa must be done by a SAQCC-registered technician. Adding gas without fixing the leak is a temporary fix that keeps costing you.

Q: How much does it cost to fix an aircon that is not cooling?

A: It depends on the cause — from nothing if a filter was the problem, to a larger repair for a compressor. A technician diagnoses first and quotes in writing before any work starts.

Do not spend another warm night waiting

A unit that is not cooling properly will only get worse as summer peaks, and the longer a fault runs, the more expensive it becomes. If you are in Kariega, KwaNobuhle, Despatch, Gqeberha or anywhere in the wider Nelson Mandela Bay, Leon's Air Conditioning diagnoses and repairs aircons across all major brands — call 041 992 3363 or request a quote online, and get the system checked before the next heatwave.