Split System Not Cooling? 10 Common Reasons & How
to Fix Them

Are you having split system issues in Melbourne? A split system air conditioner that’s running but not cooling properly is more than just frustrating, especially in the peak of Australian summer. It can be downright unbearable.

Whether your home feels muggy, the airflow seems weak, or the temperature just won’t drop, a struggling split system can quickly impact comfort, productivity, and even your energy bills.

Here’s some good news: Many cooling issues are common and often preventable with regular maintenance. The bad news? Some problems can lead to serious damage if ignored.

In this guide, we’ll walk you through 10 of the most common reasons your split system isn’t cooling, what you can check yourself safely, and when it’s time to call in a professional technician.

If you’re ready for a split system service in Melbourne, contact us today! 

Air filters trap dust, pollen, pet hair, and other airborne particles. Over time, they become clogged and restrict airflow. When airflow drops, your system struggles to move enough cold air into the room, making it feel like the unit isn’t cooling at all.

• Weak airflow
• Musty or dusty smells
• System running longer than usual
• Higher power bills

Most split system filters can be removed and cleaned with warm water every 4 to 6 weeks during heavy use. Let them dry completely before reinstalling, to avoid further issues like mould.

If the system still isn’t cooling after cleaning the filters, there may be deeper airflow or refrigerant problems requiring professional diagnosis and a split system service.

Refrigerant is the substance responsible for absorbing heat from indoors and releasing it outdoors. If your system has a leak or was undercharged during installation, cooling performance drops dramatically.

• Warm air blowing from the unit
• Ice buildup on the indoor or outdoor unit
• Hissing sounds
• The system runs constantly without reaching the set temperature

Unfortunately, nothing. At least not safely. Refrigerant handling must be done by a licensed professional due to environmental and safety regulations.

A split system technician will locate the leak, repair it, and recharge the system correctly. Simply “topping it up” without fixing the leak leads to repeat failures and potential compressor damage.

Sometimes the problem isn’t your air conditioner at all… It’s the control system. Incorrect thermostat settings, dead remote batteries, or faulty sensors can all prevent proper cooling.

• The system starts and stops unexpectedly
• The temperature doesn’t match the setting
• The unit doesn’t respond to remote commands

• Replace the remote batteries
• Ensure the unit is set to cooling mode, not fan or dry
• Double-check temperature settings

If the internal temperature sensor or control board is faulty, professional testing and repair are required.

The outdoor unit releases heat from inside your home. If it’s clogged with leaves, dust, grass clippings, or even animal nests, it can’t expel heat efficiently, leading to poor cooling performance. And let’s face it… split systems in Melbourne have to contend with quite a lot of outdoor pressure.

• The system struggles during hot weather
• The outdoor fan seems loud or strained
• The unit frequently shuts down

• Gently clear debris around the unit
• Maintain at least 30–50 cm of clearance
• Avoid using high-pressure water directly on coils

Deep coil cleaning, bent fins, and electrical faults inside the outdoor unit require specialist tools and training. Always rely on a split system service expert to avoid injury or further damage to the unit.

Evaporator coils absorb heat. If airflow is restricted or refrigerant is low, the coils can drop below freezing and develop ice (yes, even in Australia), greatly reducing cooling performance.

• Ice on the indoor unit
• Weak airflow
• Water leaks after the ice melts
• The system stops cooling suddenly

• Turn off the unit and allow the ice to melt
• Check for dirty filters
• Ensure vents are open

Frozen coils are often symptoms of deeper issues like refrigerant leaks or failing fans, problems that worsen if ignored. Professional split system diagnosis and service can keep your unit running when you need it most.

If your split system is too small for your room size, ceiling height, insulation level, or sunlight exposure, it will struggle to cool effectively, especially during heatwaves.

• You run the system constantly
• Indoor temperature never reaches the target
• Rooms feel unevenly cooled
• High electricity bills

Unfortunately, this isn’t something filters or settings can fix. Proper load calculations should be done by a qualified Melbourne split system professional.

An HVAC technician can assess your space and recommend resizing, zoning, or upgrading for proper performance and efficiency. When the alternative is high costs and endless discomfort, why would you not seek professional help?

Capacitors help start compressors and fans. When they weaken or fail, motors may not start or might run inconsistently, reducing cooling capacity.

• Humming noises
• The outdoor fan is not spinning
• The system struggles to start
• Intermittent cooling

DIY electrical repairs are dangerous and can void warranties. You definitely shouldn’t attempt them yourself.

Licensed split system experts use meters and safety protocols to test, replace, and verify correct electrical operation.

Your split system removes moisture from the air. That water drains through a small pipe. If the drain becomes blocked, water can back up into the system and trigger safety shutoffs, a huge inconvenience for owners of a split system in Melbourne during Summer.

• Water leaks from the indoor unit
• The system stops unexpectedly
• Musty smells

You can sometimes clear minor blockages with a wet/dry vacuum or by gently flushing the line with water.

If blockages persist or water damage is present, professional cleaning and inspection are essential to prevent mould and electrical hazards.

In systems with multiple indoor heads or ducted elements, airflow imbalance, leaks, or faulty dampers can prevent proper cooling distribution.

• Some rooms are cool, others aren’t
• Weak airflow in certain areas
• Whistling sounds in the walls or ceiling

Check that internal vents are open and unobstructed.

Airflow balancing, pressure testing, and duct sealing require specialised diagnostic tools that only split system service experts are likely to have.

One of the biggest reasons split systems stop cooling properly is simple neglect. Dust buildup, refrigerant loss, worn components, and electrical wear all develop gradually (and silently) over time. That’s where split system service technicians come in.

• Reduced cooling capacity
• Rising electricity bills
• Shortened system lifespan
• Unexpected breakdowns
• Voided manufacturer's warranty

An annual professional service keeps your system operating at peak efficiency and catches small issues before they become expensive repairs.

Even the most well-maintained split system in Melbourne will eventually need professional attention. Licensed air conditioning technicians don’t just “clean” your unit; they perform a full system health check, including:

• Refrigerant pressure testing
• Electrical component inspection
• Coil deep cleaning
• Drainage testing
• Fan and motor performance checks
• System efficiency measurements

Regular maintenance leads to:

• Better cooling performance
• Lower power bills
• Longer system life
• Fewer emergency breakdowns
• Healthier indoor air quality

You should stop using your system and call a licensed technician if you notice:

• Warm air is blowing constantly
• Ice buildup on the indoor or outdoor unit
• Burning smells or electrical odours
• Loud grinding, buzzing, or rattling noises
• Water leaking into walls or ceilings
• System tripping circuit breakers

These symptoms can indicate serious mechanical or electrical issues that worsen rapidly if ignored.

While professional servicing is essential, here are a few habits that help keep your system in top shape between visits:

• Clean filters monthly during heavy-use seasons
• Keep the outdoor unit clear of debris
• Don’t block indoor vents with furniture
• Avoid extreme temperature settings
• Run your unit regularly to prevent stagnation
• Book yearly professional maintenance

If your split system isn’t cooling properly, it’s not just an inconvenience; it’s usually a warning sign. Small issues like dirty filters or blocked drains can escalate into major compressor failures, refrigerant leaks, electrical faults, or complete system breakdowns.

While a few basic checks can be done at home, most cooling problems in Melbourne require trained, licensed professionals to fix safely and correctly. Regular professional maintenance not only restores proper cooling, it protects your investment, reduces power bills, and ensures reliable comfort when you need it most.

If your split system is underperforming, noisy, leaking, or simply not keeping up anymore, the smartest move is to book a professional inspection before a small problem turns into a costly replacement.

Need a same-day split system assessment in Box Hill, Blackburn, Lilydale, Kew, Vermont, Balwyn, Ringwood, Rowville, Malvern, Yarra Glen, or Toorak? Visit our showroom and warehouse in Chirnside Park to see our full range of air conditioning solutions. 

If you’re ready for a quote, call us on 03 9726 4444, email admin@austclimate.com.au, or head to our contact page. We’ll soon have your system back in peak form!