To troubleshoot an air conditioner not cooling, start with the simple checks first. Confirm your thermostat or controller is set to cool mode at a low enough target temperature, check that the air filter is not clogged, make sure no ice has formed on the evaporator coil, and walk outside to confirm the outdoor unit is running and not blocked by leaves or debris. If those quick checks do not solve it, the next likely causes are a refrigerant leak, dirty condenser coils, a tripped circuit breaker, leaking ductwork, an undersized system, or a mechanical issue with the compressor or capacitor. The first four checks you can usually do yourself in under fifteen minutes. Anything beyond that, including refrigerant work and electrical diagnostics, needs a licensed technician.

At AC Store, Steve, James and the team get calls about systems not cooling all year, with a noticeable spike on the first hot weekend of summer. After thousands of service calls across Brisbane, North Lakes, Sunshine Coast, Carindale and Moreton Bay, we have seen every possible reason a unit refuses to cool. Here is a complete, step by step guide to working out what is wrong, what you can fix yourself, and when it is time to call us in.

Quick Diagnostic: Where to Start

Before you assume the worst, run through these five quick checks. They take about ten minutes total and resolve more than half of the “not cooling” calls we receive.

Check the controller. Confirm it is set to cool mode (snowflake icon), the target temperature is below the current room temperature, and the fan is set to auto or high. Remote control batteries are also a surprisingly common culprit.

Check the filter. Pull the front panel off your indoor unit and look at the filter. If it is grey, hairy or visibly clogged, that is your first answer.

Check the outdoor unit. Walk outside and confirm the outdoor unit is running. Listen for the compressor and the fan, and feel whether warm air is being expelled from the top.

Check the breaker. Look at your switchboard. If the AC circuit has tripped, switch it back on and see if the unit returns to normal operation.

Check the controller temperature reading versus actual room temperature. If the reading on the controller is wildly different from a thermometer in the room, the sensor may be the issue.

If none of those resolve it, you need a deeper troubleshoot. Read on.

Common Reasons Your Aircon Is Not Blowing Cold Air

Most “not cooling” issues trace back to one of ten common causes. Here is what each looks like, what you can check yourself, and when to call in our team.

1. Wrong Thermostat or Controller Settings

The most common reason an air conditioner is not cooling is a settings issue, not a fault. The unit might be in fan only mode, the target temperature might be set above the room temperature, the timer might be running a heating program from winter, or the controller batteries might be flat.

What to check: confirm cool mode, set the temperature to 21 to 23 degrees, set fan to auto, replace remote batteries, and clear any active timers. Smart Wi Fi controllers can sometimes lose configuration after a power outage, in which case a quick reset usually fixes it.

2. Dirty or Clogged Air Filter

A blocked filter is the single most common cause of poor cooling performance. As the filter fills with dust, pet hair and skin cells, less air can pass through. The unit may still feel like it is running, but airflow drops, the coil ices over, and the room never cools properly.

What to check: pull the filter, hold it up to the light. If you cannot see clearly through it, wash it in warm soapy water, let it dry fully, and reinstall. For ducted return air filters, replacement is often the better option.

3. Ice Build Up on the Evaporator Coil

If you see ice on the indoor coil or on the refrigerant lines, your system has frozen up. This usually happens after extended running with low airflow (caused by a clogged filter), low refrigerant, or a fan motor that is not spinning at the right speed. A frozen system cannot cool because the coil cannot exchange heat with iced water on top of it.

What to check: switch the system off, leave it off for two to three hours so the ice can fully thaw, dry the area below the indoor unit, then run a fan only cycle. If ice returns, you have a deeper problem and need a technician.

4. Dirty or Blocked Outdoor Condenser Unit

The outdoor unit dumps heat from inside your home to the outdoor air. If the coils on the outdoor unit are choked with dust, lawn clippings, leaves, spider webs or pollen, it cannot release heat fast enough, and cooling performance suffers. Outdoor units that sit close to gardens, fences or air vents are particularly prone.

What to check: switch the system off, gently brush off visible debris, hose down the fins from outside in (never use high pressure), clear leaves from around the unit, and confirm there is at least 30 to 50 cm of clearance on all sides. Avoid bending the delicate aluminium fins.

5. Refrigerant Leak or Low Charge

Refrigerant is the lifeblood of your air conditioner. If the system is low on charge because of a leak, the unit can run for hours but never cool properly. You may notice the indoor coil icing up, hissing sounds near the indoor or outdoor unit, oily residue on copper pipes, or warmer than usual air from the vents.

What to check: nothing safely. Refrigerant work is regulated and licensed only. If you suspect a leak, switch the system off and book a repair appointment. Our technicians will locate the leak, repair it, evacuate the lines and recharge with the correct refrigerant.

6. Power Supply Issues

Sometimes the system is not cooling because part of it is not getting power. The indoor unit might run on its own circuit and the outdoor on another, and a single tripped breaker can leave the indoor blowing room temperature air while the compressor sits idle. Loose wiring, a faulty isolator switch or a fault on the outdoor electrical board can also cause this.

What to check: look at the switchboard for tripped breakers, reset once, and observe whether it trips again. If it does, switch it off and call a technician. Repeated tripping points to a fault that needs investigation, never just keep resetting.

7. Aircon Undersized for the Space

If your unit is genuinely too small for the room or the home, it will run flat out without ever reaching the set temperature. This is most common when a system was installed for a smaller home that has since been extended, when a 2.5 kW split has been asked to cool a 40 square metre open plan area, or when ducted capacity was sized aggressively low to save money on the original quote.

What to check: count the floor area of the space the unit is meant to cool, and compare to what the system is rated for. As a rough rule, you need around 0.15 kW per square metre in a Queensland home. If you are well undersized, a replacement or supplementary unit is the only real fix. Request a split system quote for a single room solution.

8. Mechanical Faults

Fans, motors, blower wheels, capacitors and contactors all wear over time. A failing fan motor on the indoor or outdoor unit dramatically reduces cooling. A faulty capacitor on the compressor can stop the outdoor unit from starting properly. Blocked drain pumps can shut the unit into protection mode.

What to check: listen for unusual sounds, buzzing, clicking, grinding or screeching. Watch for outdoor units that hum but do not start fan rotation. These are all signs of mechanical wear that need professional attention.

9. Leaking or Damaged Ductwork

In ducted systems, leaking ducts are a hidden cause of poor cooling. Cool air escapes into the roof cavity instead of reaching your rooms, while the system runs harder to compensate. You may notice some rooms cooling fine while others stay warm, the unit running constantly without reaching set temperature, or noticeably higher running costs over time.

What to check: not much from the ground. Duct inspection requires roof cavity access and is a job for a technician. If you have a ducted system that is not cooling evenly, a duct inspection during your annual service usually identifies the issue.

10. Compressor or Capacitor Problems

The compressor is the heart of your air conditioner. If it fails, the system simply cannot produce cold air. Common signs are an outdoor fan that runs without the compressor humming, a unit that hums for a few seconds then trips the breaker, or a complete absence of any sound from the outdoor unit.

What to check: nothing safely from your end. Compressor and capacitor diagnostics require electrical testing tools and refrigeration knowledge. Older units (over 10 to 12 years) with compressor failure often cost almost as much to repair as to replace, so a technician will usually present both options.

Symptom to Cause Matrix

Symptom	Most Likely Causes	DIY Possible?	Pro Recommended?
Indoor unit running, room not cooling	Settings, dirty filter, low refrigerant	Partial (settings, filter)	Yes for refrigerant
Ice on indoor unit or pipes	Low refrigerant, blocked airflow, fan fault	Thaw and check filter	Yes if it returns
Outdoor unit not running	Tripped breaker, capacitor, contactor, electrical fault	Reset breaker once	Yes if it trips again
Strange noises (buzzing, grinding)	Fan motor, capacitor, debris in unit	Visual check only	Yes
Some rooms cool, others not (ducted)	Leaking ducts, zone faults, dampers	No	Yes
Unit runs constantly never reaches setpoint	Undersized, low refrigerant, leaking ducts	No	Yes
Burning or chemical smell	Electrical fault, refrigerant leak	Switch off	Urgent
System trips breaker repeatedly	Compressor, electrical, motor fault	Switch off	Urgent
Warm air from vents	Refrigerant leak, frozen coil, settings	Settings and filter only	Yes
Loud humming with no cooling	Capacitor or compressor failing	No	Urgent

Step by Step DIY Troubleshooting Guide

If you want to work through the issue yourself before calling a technician, here is the order we recommend.

Step 1, settings check. Cool mode, target temperature below room, fan auto, no active timers, fresh remote batteries.

Step 2, filter inspection. Remove and clean or replace if dirty. Wait until fully dry before reinstalling.

Step 3, breaker reset. Once only. If it trips again, stop and call a professional.

Step 4, outdoor unit check. Confirm it is running, fan rotating, exhaust air feels warm, no debris around it.

Step 5, ice check. If the indoor coil or pipes are iced, switch off for two to three hours to thaw fully, then run fan only.

Step 6, leak check. Look for hissing sounds, oily residue on pipes or moisture pooling under the indoor unit.

If you have run through all six steps and the system still is not cooling, the issue is beyond DIY. Time to book a service and let a qualified technician take a look.

Things to Know Before You Call a Technician

A small amount of preparation makes service calls faster and cheaper. Here is what helps.

Note when the issue started. A sudden change after a storm or power outage points one way. A gradual decline over weeks points another. Either piece of information helps the technician zero in on the cause.

Document the symptoms. Are some rooms cooling but not others? Is the outdoor unit running? Are there sounds? When does the issue happen, only at peak heat or all the time? Write it down before the call.

Have the model number ready. The system’s model number is usually on a sticker inside the front panel or on the side of the outdoor unit. Sharing it during booking lets us bring the right parts on the first visit.

Check warranty status. If the unit was installed by AC Store within the last 5 years, you are likely still under our warranty, and many issues are covered.

Clear access. Make sure the indoor unit is reachable, the outdoor unit area is clear of furniture, and the manhole to the roof cavity (for ducted) can be accessed without moving heavy items.

DIY vs Professional Fixes

Task	DIY Friendly	Professional Recommended	Notes
Adjusting controller settings	Yes	No	First check every time
Replacing remote batteries	Yes	No	Surprisingly common fix
Cleaning split system filter	Yes	No	10 minutes, every 4 to 8 weeks summer
Hosing outdoor coil debris	Yes (gentle hose only)	Optional	Never use high pressure
Resetting tripped breaker	Yes (once only)	Yes if repeats	Repeats indicate fault
Thawing iced coil	Yes	Optional	If returns, call pro
Replacing return air filter (ducted)	Yes	Optional	Every 3 to 6 months
Refrigerant top up or leak repair	No	Yes	Licensed work only
Capacitor or motor replacement	No	Yes	Electrical and mechanical
Ductwork inspection or repair	No	Yes	Roof cavity access
Compressor diagnostics or replacement	No	Yes	Major repair, replacement may be cheaper
Annual full service	No	Yes	Maintains warranty and efficiency

Sometimes the most cost effective answer is replacement, not repair. Here are five signs your unit is at the end of its life.:

It is over 12 to 15 years old. Most residential systems are designed for 15 to 20 years of service, but older units lose efficiency every year. A new system can pay for itself in lower running costs alone.

You are paying for repair after repair. If you have spent more than half the cost of a new system on repairs in the last two years, replacement is usually the smarter call.

The unit uses old refrigerant. Systems running R22 are difficult and expensive to recharge in 2026. Replacement with a modern R32 unit is often the better long term move.

Cooling is uneven and the system never quite catches up. Undersized systems and tired compressors both produce this symptom, and both point to replacement.

Running costs are climbing. Modern inverter systems are dramatically more efficient than older fixed speed units. If your bills are creeping up while temperatures stay the same, an upgrade is worth costing out.

If any of these apply, request ducted air conditioner quotes for whole home replacement, or a split system quote for single room upgrades. We always present repair and replacement options side by side so you can decide based on real numbers.

How AC Store Can Help

At AC Store, we are more than just an air conditioning retailer. We are a local Queensland team committed to keeping families comfortable year round. Led by Steve and James, our business has grown into one of the state’s most trusted names for ducted air conditioning and split system installations across Brisbane, North Lakes, Sunshine Coast, Carindale and Moreton Bay.

When you call us about a system that is not cooling, our technicians arrive prepared to diagnose properly, explain what they find, and quote any repair upfront with no surprises. We carry common parts on the van so many issues are fixed on the spot. We are honest about whether repair or replacement makes more sense, and our advice is the same advice we would give our own families. If the issue is more involved and the unit is past its useful life, we will design a replacement that is sized correctly for your home and matched to your budget.

Ready to Get Your Home Cool Again?

An air conditioner not cooling is one of the most frustrating problems a Queensland homeowner can face, especially when the temperature outside is climbing. The good news is most causes are fixable, and the few that are not are signs that an upgrade will deliver better comfort and lower running costs for years to come.

Whether you live in Brisbane, North Lakes, Burpengary, Caboolture, Palmview, Buderim, Deception Bay, Carindale, or anywhere across the Sunshine Coast and Moreton Bay, Steve, James and the AC Store team are ready to help. Book a service today and get your home back to the comfortable temperature you deserve.

Frequently Asked Questions