Air conditioning running but not cooling — what is going on?
If your air conditioning unit is switched on and running but failing to cool the room, the cause is usually one of a handful of common issues. Some can be resolved without a call-out; others require a qualified F-Gas engineer. Here is what to check first.
1. Dirty or blocked air filter
The most common cause of poor cooling is a blocked air filter. Most split system indoor units have a washable filter behind the front panel that should be cleaned every 4–6 weeks during periods of heavy use. A heavily clogged filter restricts airflow, making the unit work harder while delivering less cool air. Check and clean the filter before anything else.
2. Low refrigerant (gas leak)
Refrigerant (commonly R32 or R410A) is the fluid that carries heat out of your room. If there is a leak in the system, refrigerant levels drop and cooling performance falls significantly — the unit may also ice up on the indoor coil or make a bubbling/hissing noise. Only an F-Gas certified engineer can legally recharge the system, and the leak must be found and repaired first.
3. Iced-up indoor or outdoor coil
If the indoor unit's coil has frozen, the unit will blow air but deliver little or no cooling. Switch the unit off and let it defrost fully (usually 2–4 hours), then clean the filter and restart. If it ices up again, there is likely an underlying issue — low refrigerant, poor airflow or a faulty component — that requires an engineer.
4. Outdoor unit blocked or in direct sun
The outdoor unit needs clear airflow to reject heat effectively. Check that nothing is obstructing the front of the unit — overgrown plants, stored items or debris. Units in direct afternoon sun also work harder. In extreme hot weather, efficiency drops for all systems.
5. Incorrect settings or mode
Check that the unit is set to cooling mode (usually a snowflake symbol) rather than fan-only or heating mode. Also check the target temperature is set lower than the current room temperature.
When to call an engineer
If the filter is clean, settings are correct and the unit is still not cooling effectively, it is time to call a qualified engineer. A refrigerant leak, faulty compressor, failed capacitor or blocked outdoor coil all require professional diagnosis and repair. Get free quotes from local AC engineers here.