Call us for a free quote 1300 13 40 41

Air Conditioner Freezing Up

Imagine you’ve come inside after bearing the heat and humidity of a typical Australian Summer’s day.  You crack open a cold one, poor over ice, and sit back to relax.  But your still hot and sticky.  The cool drink is helping, but the AC is not.

So, you turn the temperature right down.  Wait.  No change.  Give me a break!

You’ve heard that turning the air conditioner off and on again can help kick it back into gear, so you head out to the condensing unit.  Then you notice ice at the outdoor unit!  This is not right.  The only ice you want to see is in the beverage of your choice.  What do you do?

An air conditioner freezing up is a sign of an underlying issue.  It could be minor and resolved with a few checks and adjustments.  However, it could also be a sign of a major issue or even end of life for an older split system air conditioner icing up.

Fortunately, there are simple checks and DIY aircon maintenance tasks that you can do if you do find ice on your air conditioning system.  We’ll go through the most common reasons for air conditioner icing up, quick fix for AC freezing up, and how you can prevent this issue in future.

This week’s question:  

Why is my air conditioner freezing up?

Air conditioners freeze up for many different reasons.  Many issues have solutions, some of which you can carry out yourself.  Here is the summary:

Low Evaporator Coil Temperature

The primary cause of ice in an air conditioner is low temperature in the evaporator coils.  Start by checking temperature settings and ensure it’s not set too low.  In Summer, 24 degrees on cooling is sufficient.  If set lower than this, try increasing the set temperature and re-running (once the ice has been cleared).  However, there are many other factors that impact coil temperature, including air flow and pressures.

Restricted Air Flow

Restricted air flow is a common cause of air conditioner freezing up.  Dirty return air filters, blocked coils, and/or collapsed duct are all typically ways air flow is reduced within an air conditioning system.  Check, remove, and clean filters as needed.  If safe to do so, also check coil conditions and ductwork.  An HVAC professional is recommended to clean coils and/or repair ductwork, in the interest of safety (for you and your AC system).

Woman comparing dirty and clean return air filters for wall split system

External Obstruction

Blockages to air flow can also be external to the air conditioner.  Anything preventing airflow and/or adequate heat exchange can cause AC coils to get too cold and start to freeze.  Check and ensure suitable clearance around all sides of an air conditioning unit.

Faulty Thermostat

Sometimes the temperature issue comes from a malfunctioning thermostat.  If a thermostat is faulty, the temperature settings, detection, and/or feedback to the rest of the system may be incorrect.  Check if your thermostat (typically in the form of a controller) is responding normally.  If not, try replacing batteries or testing another controller (in the case of multi split systems).  If still no luck, the thermostat likely needs repairs or replacement.

Environmental Temperature Drop

In colder external conditions, ice formation is more likely.  This may occur overnight or early hours of the morning in some inland areas and regions of Australia where air temperature drops dramatically.  In this instance, it’s recommended to open windows and/or using the AC in fan mode to help thaw the ice or prevent development.

Blocked Condensation/Drain Line

When an AC drain line is clogged, water can’t escape properly.  In turn, it may freeze near the evaporator coil.  Regular maintenance of an air conditioner is essential, calling in the experts to clear and clean the condensation line on a routine basis.

Low Refrigerant Pressure

Many people are aware that an aircon short on gas may ice up.  Refrigerant is an essential part of how a modern-day reverse cycle air conditioning system works.  This is an issue that requires a fully licenced HVAC technician to diagnose and resolve.

Damaged Blower Fans

Blower fan issues can reduce airflow and pressure, which can both lead to freezing of the refrigerant lines and/or coils.  The issue may be with the fan motor, the propeller, the shaft, fan capacitors, or combination of these components.  Use your ears and eyes to assess (where safe), but repair or replacement is best left to a professional.

ducted air conditioner icing up indoor coil faulty fan blower

As you can see, there are many possible causes of an air conditioner freezing up.  Sometimes it may just involve one issue (e.g. low gas pressure).  Sometimes it can be a combination of issues causing the ice formation (e.g. dirty filters, blocked drain line, and restricted coils).

Understanding these factors are key to addressing ice build-up in you air conditioning system.  Treating the root cause of air conditioner issues will help ensure efficient and effective operations and system longevity.


Quick fix for AC freezing up (20 point check).


If you’re stuck with ice in all the wrong places this Summer, don’t fear – help is here!  There are some simple steps that can offer a quick fix for AC freezing up in many cases.  However, there may be a point where professional help is required if the DIY steps do not resolve the issue.

  1. Turn the AC off at the controller and isolator outside,
  2. Allow the ice to defrost and put down towels where suitable,
  3. Check and clean air filter if dirty,
  4. Check the coils and note if cleaning required,
  5. Check your vents and ensure open and undamaged,
  6. Check ductwork and look for any damage or restrictions,
  7. Check and remove any airflow obstructions from any units,
  8. Check your condensate drain line has been flowing correctly and water exiting as normal,
  9. Once all checks completed and safe to do so, turn the AC back on,
  10. Check the thermostat or controller is operating and responding as normal,
  11. Check settings and ensure no lower than 22 in cooling (24-27 degrees recommended for efficiency),
  12. If not confident that all ice has melted, turn system onto Fan Mode only,
  13. Monitor the system,
  14. Listen out for any unusual noises and recording them if you can,
  15. Watch out for any signs of water leaking or ice returning,
  16. Call in an HVAC contractor for next level service, including professional checks*,
  17. *Check blower fan operation (HVAC contractor only),
  18. *Check refrigerant levels (HVAC contractor only),
  19. *Chemically clean coils if required (HVAC contractor recommended), and,
  20. *Complete AC service as per DA19 Australian Standards (HVAC contractor only).


While some ice build-up issues can be resolved with DIY methods, others require the expertise and experience of an HVAC technician.  Regular maintenance is the key to preventing most air conditioner issues, and that includes your aircon turning into a mini ice station!


Father and son completing air conditioning repair service on wall split system inc gas pressure check


How do I keep my air conditioner from freezing up?

To help prevent your air conditioner from freezing up in the first place, some pre-planning and routine maintenance is required.  Follow these simple tasks to help prevent your aircon icing up:

  • Check your AC settings and ensure not running the system too cold (remember, 24+ degrees in Cool mode recommended in Summer),
  • Completed monthly or at least seasonal air filter checks and clean or replace where required,
  • Carry out regular AC service for many reasons where safe and competent to do so,
  • Arrange periodic professional aircon service (anywhere from monthly for commercial preventative maintenance to annually for a standard home air conditioner),
  • Approve repairs if/when recommended, e.g. reinsulating pipework, replacing indoor fan motor when bearing start to fail, chemically clean dirty coils, etc.), and,
  • Ensure home maintenance upkeep, including clearing foliage around condenser and removing any items stored around a unit.


Stay cool and ice-free with these simple steps.  Please don’t hesitate to reach out to professionals when needed.  Also remember safety first when dealing with an electrical device such as an air conditioner.

Your comfort and air conditioner efficiency are paramount, especially in Brisbane’s hot and humid climate.  Effective and reliable air conditioning is really a necessity, rather than a luxury, in a typical Queensland Summer.  Let’s keep the ice in the drinks, not the AC!


Need help defrosting your air conditioner and cooling your home or business again?  Book your aircon repair or service today.