Air Conditioner Not Cooling Properly: How to Diagnose and Fix Common Problems

Your air conditioner is running but the room isn't getting cool. This is a frustrating problem, especially in a Sydney summer. Before you call a technician, there are several things you can check yourself — and many of these are simple fixes.

1. Check the Temperature Setting and Mode

This sounds obvious, but it's worth confirming. Make sure:

• The mode is set to COOL (not FAN, HEAT, or AUTO on a humid day)
• The set temperature is lower than the current room temperature
• The fan speed is set to AUTO or HIGH

2. Clean or Replace the Air Filter

This is the most common cause of poor cooling. A blocked filter restricts airflow, reduces efficiency dramatically, and can cause the system to freeze up.

How to check:

• Open the indoor unit's front panel (usually clips open from the bottom)
• Remove the filter(s) — there are usually two
• If they're visibly grey or dusty, they need cleaning

Wash filters under warm water, let them dry completely, and reinstall. This alone often restores full cooling capacity. Clean filters monthly in summer.

3. Check the Outdoor Unit

Go outside and check the outdoor condenser unit:

• Is the fan running when the system is on?
• Is the unit blocked by garden furniture, plants, or debris?
• Are the fins (the louvred surfaces) blocked with leaves or dirt?
• Is the unit in direct, unshaded sun all day? This reduces efficiency.

Clear any obstructions from around the outdoor unit. The fins can be gently cleaned with a soft brush or low-pressure hose.

4. Check for Ice Formation

Feel around the indoor unit's air outlet and the pipes leading to the outdoor unit. If you notice ice or frost forming:

• Turn the system off and let it thaw for 30–60 minutes with just the fan running
• Check the filter — a blocked filter is the most common cause of icing
• If icing continues after cleaning the filter, the system may be low on refrigerant, which requires a licensed technician

5. Is the Room Getting Adequate Airflow?

• Keep doors to uncooled rooms closed
• Ensure vents in the indoor unit are open and directing air correctly
• Check if ceiling fans are helping to circulate cool air (run them in reverse in summer to push cool air down)

6. Is the System Sized Correctly for the Room?

An undersized system will struggle in extreme heat. A 2.5kW unit cooling a 30m² bedroom will work fine. The same 2.5kW unit trying to cool an open-plan 60m² living area will never keep up. If your system has always struggled, it may simply be undersized.

When to Call a Technician

Call a licensed HVAC technician if:

• The system is icing up repeatedly after filter cleaning
• You can hear unusual sounds (hissing, clicking, grinding)
• The outdoor unit's fan isn't turning
• The system is tripping circuit breakers
• It's more than 3 years old and hasn't been professionally serviced

Thinking About a Replacement?

At Oceania Appliances, we carry a range of reverse cycle split systems at great prices. If your current unit is old and struggling, upgrading may be more economical than repeated repairs.

Oceania Appliances
2/14 Centre Place, Wetherill Park NSW 2164
Phone: 0481 243 211
Open 7 days, 10am – 8pm
Free delivery across Sydney