Why is my air conditioner not working?

When your air conditioning unit stops working, it might be a simple fix. But it can also be a major issue. While some problems can be avoided with regular cleaning, it’s important that you have a technician look at the issues you can’t solve yourself. There are a variety of reasons that can set your air con off, so let’s have a look at some of the most common ones.

6 Common Air Con Problems

There are a number of reasons as to why your air conditioner has stopped working, including one or more of the following:

  • Unit is unplugged
  • Blocked filters and coils
  • Thermostat out of place
  • Blown circuit breakers and fuses
  • Ice buildup
  • Wrong settings

Let’s now dive into these in more depth.

Wall switch

First and foremost, check the unit is plugged in! While this might be an obvious issue, on occasion the plug may have come partially or completely dislodged. Perhaps it was the dog or kids, but nevertheless it might be exactly the reason why your air con isn’t running.

Blocked filters and coils

Blocked filters and coils

Inadequate maintenance is a common factor for an AC to break down. If you leave your filters and air conditioning coils unclean it’s possible for the compressor or fans to fail prematurely, so it’s important to clean filters periodically. Washable filters should at least be cleaned annually to help keep your air con running, but you might like to clean them every three to six months if you find that they’re typically covered in a lot of dust and dirt when you take them out. Aim to clean them before peak seasons – summer and winter – to help your air con run efficiently during these times.

Room air conditioners are also designed with a thermostat sensor (located behind the control panel), which measures the temperature of the air the unit is blowing out. If your unit is not blowing any cold air, the sensor may have been knocked out of its position. This requires a technician to adjust it back to its right place.

In addition, check the thermostat status on the controller. If it’s set to ‘on’, make sure the thermostat is also set to ‘cool’ (read your manual if in doubt how). You might need to lower the temperature on your controller.

Circuit breakers and fuses

Circuit breakers and fuses

Check to see if the fuse has been blown or if the circuit breaker has been tripped and ensure they’re turned on and functioning correctly. With older homes, it can be common to have circuits that are overloaded if the air con shares a circuit with other appliances such as fridges, microwaves or irons.

Ice build-up

Another common issue is ice build-up. It may be possible that ice has formed inside the unit, causing a low cooling performance. To check if this is the case, switch off the unit and lift the cover to see if there is any ice build-up on or behind the filter. This typically occurs if the fan blower belt is damaged.


air conditioner settings

Having the right temperature set on your control is key. If your AC is blowing air but still isn’t cold, ensure your unit is set to ‘cooling’ mode on the controller. Typically, this is indicated by a snowflake symbol or the words ‘cold’ or ‘cool’. If it’s already on this mode, check the temperature is low enough for the unit to know it needs to cool. You can test this by dropping the temperature to 16°C on a hot day to check if the air from the air con feels cool before you switch it to an optimum level such as 24°C. This goes for heating as well – if you’re using the air conditioner to heat the home in winter but it’s blowing cold air, check the mode on your controller. Key settings to remember:

  • Snow flake = cooling
  • Sun = heating

During the heating cycle, it’s possible for the unit to blow cold air. This might occur because of the defrost cycle, which switches to a ‘cooling’ mode to allow the outdoor unit to heat up and defrost. However, there might also be settings on the controller that are hindering the fan to switch off – this is where you can consult your manual or a technician. It might also be because some controllers allow you to set the fan motor to constant operation, meaning the fan will operate regardless of settings, defrost cycle or temperature, which you can switch off.


Compressor and fan controls can wear out overtime, particularly if your unit is constantly getting switched on and off. It’s also common for a compressor to stop working due to a faulty or broken capacitor. An air conditioner can’t work without a functioning compressor, so it might need to be replaced.

Signs your air conditioner might not be working properly


How to check your air conditioner is working properly

In some cases, you might hear various noises from your air con. This might be due to air filters being dirty, giving the AC a more difficult time processing the air. Another problem might be that the grille is not fitted properly, which can cause the air to bypass the grille and create a ‘whistle’ noise when the fan is on.

Ensure to keep filters clean and centred on the grille to prevent any air gaps. It’s also important that if you’re replacing the grille, it’s the right size for the unit as undersized return air grilles can make the AC work harder than it should, causing the unit to become noisy. If the noise turns into banging or grinding, it’s recommended that you switch the unit off immediately. This might be caused by a failure in the fan motor or fan motor mounts, which require a technician to fix.

Smoke or steam

If there is steam coming out with a burning plastic or rubber smell, it’s important to switch off the unit. However, during winter, it can be common for steam to come from your outdoor unit when it’s set to ‘heating’. This is caused by the defrost cycle which melts and evaporates frozen condensation into the air, which is necessary to ensure it doesn’t turn into an ice box and prevent airflow over the radiator coil.

Water from outdoor unit

Water from outdoor air conditioning unit

During the heating and cooling cycles, refrigerated air cons are designed to remove moisture from the air. On the heat setting, there might be water on the ground near your outdoor unit (unless it’s drained to a garden bed or a downpipe) – this is because moisture is drawn from the outdoor air. However, on the cooling setting, moisture is drawn from the inside air and in turn, the water is drained out from the roof area into the gutters.

Resetting the unit

If there has been a power failure fault, temperature fault, or no cold air is blowing, you might like to try switching off the power at the fuse box. If you switch it back on, and the problem continues, record the fault shown on the controller (if stated) and provide this information to a specialist.  

Is it time to replace your air conditioner?

Air Con Replacement

If you’ve had a professional check your air conditioner and there’s simply no solution, then perhaps it’s time to buy a replacement. In general, air conditioners are claimed to last around nine to ten years.

These ice boxes are typically energy-intensive, so if your unit has had its day, then it might be worth investing in a new model. New units with high energy efficiency ratings might help reduce the running costs and might also provide you with a few extra features for your convenience.

To see which air conditioner brand is the best at helping to keep Australian families cool, follow the link below to our latest ratings report. We also have an air conditioner buying guide, which includes a few tips on how to buy the best air conditioning system for your home. 

Air Con Reviews & Ratings

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