Why Is My Air Conditioner Not Cooling? Troubleshooting Guide

There are few things more frustrating than an air conditioner that's clearly running but leaving the room warm — especially on a scorching Western Sydney afternoon. The good news is that the cause is often simple, and some fixes take five minutes. This guide walks through the common culprits, what you can safely check yourself, and when to call a professional.

Quick answer: An air conditioner running but not cooling is most often caused by a dirty air filter blocking airflow, low refrigerant (which means a leak), dirty or iced-up coils, a blocked outdoor unit, or wrong thermostat settings. Start by cleaning the filter and checking the thermostat — these solve a surprising number of cases. Refrigerant and electrical problems need a licensed technician.

Start with what you can check yourself

Before calling anyone, work through these safe checks — they resolve a lot of "not cooling" complaints:

Clean the air filter. This is the number one cause. A clogged filter chokes airflow, so the unit runs but barely cools. Remove it, clean or replace it, and see if performance recovers. In dusty areas or heavy summer use, filters clog faster than people expect.

Check the thermostat. Confirm it's set to cooling mode, not fan-only, and that the target temperature is actually below the room temperature. It sounds obvious, but it's a common oversight.

Check the circuit breaker. If the outdoor unit isn't running at all, a tripped breaker may be the cause. Reset it once — if it trips again, stop and call a technician, as that signals an electrical fault.

Clear the outdoor unit. The outdoor unit expels heat and needs airflow. Leaves, garden growth or debris packed around it will strangle performance. Clear a good space around it.

Seal the room. Open doors and windows let cool air escape and warm air in. Close them, and draw blinds or curtains against direct sun — a west-facing room copping the afternoon sun can defeat even a healthy system.

Causes that need a professional

If the basics don't fix it, the problem is likely one of these — and each requires a licensed technician:

Low refrigerant. If the system is low on refrigerant, there's a leak. Refrigerant isn't consumed in normal running, so it can't just be "topped up" — a licensed ARCtick technician must locate and repair the leak, then recharge. Handling refrigerant without a licence is illegal.

Dirty or iced-up coils. Grimy evaporator or condenser coils can't transfer heat efficiently. Sometimes a restricted system ices over, blocking airflow entirely. This needs professional cleaning and diagnosis.

Failed components. A faulty capacitor, compressor or control board will stop the system cooling and requires a qualified repair.

Why it matters to act early

A system limping along while not cooling is usually working harder than it should, which wastes energy and can worsen the underlying fault. Many of these problems — clogged coils, refrigerant issues found early, drainage blockages — are exactly what a routine annual service is designed to prevent.

If your unit is also old and this isn't the first failure, it may be worth weighing repair against replacement — see the signs it's time to replace.

When it's an emergency

If your air conditioning fails during a heatwave, that's a different situation — check our heatwave emergency guide for what to do while you wait for a technician.

Checked the basics and still no cool air? Contact BES for air conditioning repairs across Hoxton Park and South West Sydney. We'll diagnose it properly and fix it right.