7 Reasons Why Your Aircon Is Not Cooling

7, 2025 | AC Maintenance and Repair Nothing is worse than expecting a blast of beautiful cold air from your aircon, only to get a lukewarm puff instead. When the Australian heat hits, a broken air conditioner (or 'AC') is more than just annoying-it’s a real problem for your comfort and your wallet. If your aircon is running but not cooling your home or office, the cause could be something simple you can check right now, or it could be a sign of a serious issue that needs a licensed professional to fix safely and legally. We’ve put together the essential checklist for every Aussie homeowner, moving from quick checks to the big problems that need an expert. Remember, attempting to repair certain parts of your air conditioning system can be dangerous and could void your warranty. If in doubt, call a professional.

Simple Checks: Is It a Quick Fix? Before you pick up the phone and book a service call, take five minutes to rule out these easy issues. They often come down to user settings, basic blockages, or power problems. The Wrong Settings or a Tripped Circuit It might sound obvious, but it’s the number one cause of "faults." Is your thermostat or remote actually set to COOL mode? Always make sure the setting is not on FAN (which only blows existing room air) or HEAT (which, on a hot day, is a disaster!). Also, check the set temperature: if you set the temperature higher than the current room temperature, the unit won't turn on to cool. Aim for a comfortable 24°C or lower. Secondly, quickly check your main power board (switchboard). Aircon units draw a lot of electricity. On scorching days when your unit is running flat-out, the circuit breaker can sometimes trip due to a power surge. If a switch for your aircon circuit is in the 'off' position, carefully flip it back on. If it immediately trips again, do not attempt to reset it, as this indicates a serious electrical fault. Call an electrician or air conditioning technician immediately. Dirty Air Filters Are Restricting Airflow Your aircon filter is a simple mesh that catches dust, hair, pollen, and other fine particles to keep the air you breathe clean. Over time, this filter gets completely choked up. A dirty filter makes your aircon work much harder to pull air through, which drastically reduces its ability to cool the room. This can cause two major problems: Reduced Cooling: Less air gets into the system, meaning less air can be cooled and circulated. Ice Build-up: The lack of air flowing over the internal coil causes the surface to get too cold, leading to ice forming (which we discuss further down). For most split systems, you can safely remove and clean the filters yourself with warm soapy water or a vacuum cleaner. It is a key part of routine aircon care that you should aim to do at least every month or two, especially in high-use periods.

Blockages and Dirt: The Efficiency Killers If your filters are clean, dirt and debris in other parts of the system are likely the problem. These deeper blockages often require professional cleaning and servicing to fix. The Outdoor Unit (Condenser) is Choked The large box outside your house is called the condenser unit. This is the vital part of the system where the aircon releases all the heat it collects from inside your house. The side panels of the condenser are wrapped in thin metal fins (coils) that allow air to pass through and transfer the heat away. If this unit is blocked by grass clippings, leaves, dirt, or even the growth of shrubs around it, it can't release the heat efficiently. This means the system will struggle, running constantly but never achieving the cold temperatures you need. It's like having a hot engine with a blocked radiator-it simply can’t cool down. While you can safely clear away plants and wash the outside casing with a gentle hose spray, deep cleaning the delicate internal fins requires professional tools and expertise to avoid damage. Ice Build-up and the Dirty Evaporator Coil If you look at the indoor unit and notice ice or thick frost forming on the pipes, the entire coil, or even dripping water, it means something is severely restricting the airflow. This blockage usually happens when the filters or the internal coils (the evaporator) get too dirty and matted with grime. When airflow is low, the indoor coil drops below freezing point. Instead of cooling your home, the coil simply turns into a block of ice. The unit will continue to run, but no cold air will get through. If you spot this, turn the unit off immediately and let the ice melt. Then, call a professional. Ice build-up is a clear sign that a deep professional service (a "strip clean") is required to make the coils and drainage system fully operational again.

The System is Leaking Coolant (Refrigerant) Refrigerant (often called coolant or gas) is the essential chemical that cycles through your system to absorb heat from inside and release it outside. Here's the most critical piece of information: Refrigerant never runs out or gets "used up." If your aircon system is low on coolant, it means you have a leak somewhere in the piping, coils, or components. Why Is a Refrigerant Leak a Professional Job? In Australia, only a licensed and ARC-certified technician is legally allowed to handle, top-up, or repair refrigerant leaks. Refrigerant is a controlled substance. If your aircon is low on gas, the technician must: Find and fix the leak: This is the most important step. Without fixing the leak, any added refrigerant will just escape again. Safely evacuate the system: Remove any remaining gas and moisture. Re-gas the system: Refill it with the correct type and amount of refrigerant. Simply "topping up the gas" without fixing the leak is illegal, wasteful, and dangerous to your system. If a technician suggests this, you should question their qualifications.

The Airflow is Lost Before It Reaches the Room This category covers issues where the aircon is creating cold air, but that cooling power is being wasted or lost on the way to your living space. Leaks in Your Ducted System This is one of the most common issues for homes with ducted air conditioning. The cold air is produced in the main unit (often in the ceiling or under the house), and then travels through flexible ducts to reach your vents. If these ducts are old, poorly installed, or have been damaged by pests like rodents, the cold air is escaping into your hot roof cavity instead of your room. Leaking ducts can lose up to 30% of your cooling energy, making your system run non-stop for no result and sending your power bill sky-high. Only a technician can access and safely seal and repair this ductwork. The Aircon is the Wrong Size (Too Small) This is a problem that happens from day one. An air conditioner is given a 'kW' rating (kilowatt), which measures its power. If you have an undersized aircon (low kW) installed in a very large or sunny room, it will never be able to keep up with the heat entering the room. The aircon will run constantly, struggling against the heat load, often called "short-cycling." It will waste energy, wear out faster, and, most importantly, never achieve the set temperature. If your aircon has struggled to cool since the day it was installed, the unit size is likely the issue.

When to Call the Experts: Component Failures This section covers issues that are complex, expensive, and require specific technical knowledge and tools to diagnose and repair. Compressor or Fan Motor Failure The compressor is the 'heart' of your aircon system; it pressurises the refrigerant. If the compressor fails or is running poorly, the whole cooling process stops, and the unit will only blow regular air. Signs of a failing compressor include the unit making loud, strange noises (grinding or rattling) or the outside unit only running for a short time before shutting down. Likewise, if the indoor or outdoor fan motor has failed, the unit cannot move air or heat, and it will stop cooling. These problems are serious and should only be replaced by a licensed professional. Faulty Thermostat While we mentioned checking the settings in Section 1, the thermostat itself can fail. It may be misreading the room temperature, causing the aircon to switch off too early. For instance, the thermostat might think the room is 24°C when it is actually 28°C. This is often an easy fix for a technician, but you'll need them to confirm the reading with specialised equipment.

The 'AC is Fine, But House is Hot' Puzzle This is one of the most frustrating scenarios for homeowners: you’ve had a technician inspect the unit, and they report that the aircon system itself is running perfectly fine, yet your house is still hot! The Role of House Insulation and Heat Load If the air conditioner is technically working, the problem is that your house is letting in more heat than the unit can remove. This is often due to problems with the building envelope (the walls, roof, doors, and windows). Poor Roof and Wall Insulation: If your ceiling or wall insulation is old, thin, or damaged, the incredible heat from the Australian sun can pour directly into your home, overwhelming even a brand-new, powerful aircon. Leaky Windows and Doors: Gaps or worn seals around your windows and doors allow the cold air to escape and hot air to leak in constantly. The Wrong Type of Air Filter: Believe it or not, using a filter with a very high MERV rating (designed for allergy control) can be too thick for many residential systems. This 'heavy-duty' filter can restrict airflow so much that your system struggles to circulate the cold air effectively. If your aircon is technically working (the air coming out is cold), you may need to consult with a building professional to upgrade your home’s insulation and sealing, or discuss filter options with your AC technician.

Aircon Not Cooling: Frequently Asked Questions (FAQs) Here are the most common questions our customers ask about struggling air conditioning units: How can I tell if my aircon takes too long to get cold when I turn it on? A healthy aircon should typically drop the room temperature by 1 to 2 degrees per hour. If your unit runs for hours and only drops the temperature by a fraction of a degree, or it gets stuck at a certain temperature (e.g., 28°C), this is a sign it is undersized, has a refrigerant leak, or has dirty coils. Learn more about ideal AC temperature. Is it worth repairing an aircon unit that is older than 10 years? For a unit older than 10 years, any major repair (like replacing the compressor or coils) often costs close to 50% of the price of a new system. Given that new units are far more energy-efficient and come with a fresh warranty, it's usually more cost-effective in the long run to replace a unit over a decade old. How often should I clean my aircon filter when I have pets? If you have pets that shed hair, you should visually inspect and clean your aircon filters every two to four weeks-not just monthly. Pet dander and hair clog filters faster than regular dust, leading to cooling problems and reducing indoor air quality quickly. What are the signs of a refrigerant leak in my aircon system? The most reliable signs are: 1) Air coming out of the unit is only slightly cool (not cold). 2) The unit constantly runs without satisfying the thermostat. 3) You see ice or frost forming on the large copper pipe outside the unit. Why is my aircon blowing warm air even though the refrigerant has been topped up (re-gassed)? If your aircon was re-gassed and is still blowing warm air, it means the technician failed to find and fix the leak. The new refrigerant has already escaped the system. You will need to contact a different, licensed technician to perform a proper leak detection and repair before re-gassing again. Why is my car aircon not cold anymore? A car aircon system is very similar to a home system but uses different parts. The most common cause is a slow refrigerant leak in the hose or a faulty seal, as vehicle systems naturally lose small amounts over time. This requires a professional auto-electrician or mechanic to inspect, fix, and regas.

Conclusion: Your Next Step for a Cool Home When your aircon stops cooling, don't panic. Start with the simple checks: verify your settings, check your power, and clean your filters. However, once you move beyond these simple steps, remember that fixing issues like refrigerant leaks, compressor failure, or complex electrical faults is not a job for a DIY approach. These repairs are complex, require specific licenses in Australia, and, most importantly, could be dangerous. Protect your investment and your safety. If your aircon is struggling, running constantly, or showing signs of ice, it’s time to call a trusted, licensed air conditioning technician. Save our number 07 3889 4508 for any emergency aircon repair needs in Brisbane.