Why is My Air Conditioner Smoking and Making Noises in Winter?
If you live in Perth, you are likely used to mild winters…
That is until July and August hit. When inland areas like Joondalup, Midland, or the Perth Hills experience those crisp, frosty mornings dropping below 5°C, your reverse cycle system has to work overtime.
Suddenly, you might notice your outdoor unit emitting what looks like white smoke.
This is often accompanied by a sudden whooshing or hissing sound, right before your indoor unit stops blowing warm air.
Don’t panic and don’t switch the system off at the wall.
Your system isn’t broken. It is simply entering Defrost Mode, which is also known as De-Ice mode.
This is a completely normal part of operating your system safely and efficiently.
What is Defrost Mode and How Does it Work?
When heating your home in winter, your reverse cycle air conditioner essentially flips its summer operation in reverse.
It extracts heat from the outside air and transfers it indoors.
Because the outdoor air is cold, the moisture in the air condenses on the outdoor unit’s metal coils.
When the outdoor ambient temperature drops significantly, this moisture freezes instantly. This creates a layer of frost or ice over the unit.
If left alone, this ice blocks the airflow, suffocates the compressor, and stops the heating process completely.
To prevent this, modern systems use an intelligent sensor to trigger a defrost cycle.
Reversing the Cycle
The system temporarily switches back into cooling mode. It keeps the indoor fan off so it doesn’t blast you with cold air.
Melting the Ice
It redirects heat back to the outdoor coil to rapidly melt the frost.
Steam and Sounds
As the ice melts off the hot coils, it turns into harmless steam. This looks exactly like white smoke, and you will see water run-off below the unit.
The loud noise you hear is the reversing valve shifting the direction of the refrigerant gas.
Insights from the Field: The Hidden Nuances of Defrost Mode
Our service technicians spend every winter diagnosing faulty systems that are actually just defrosting.
Over the years, we have picked up a few lesser-known technical insights that change how your system behaves during a cold snap.
The Ice Anchor Blockage
Many Perth homeowners have their outdoor units installed under tight eaves or inside narrow side-passages.
If your outdoor unit is tucked away where the winter wind cannot help evaporate the moisture, it will enter defrost mode far more frequently.
Poor clearance causes the unit to re-ingest its own cold, damp exhaust air, creating a loop that speeds up ice accumulation.
The Draining Trap
A single defrost cycle can drop up to several litres of water onto the ground beneath your outdoor unit.
If your unit is mounted on brackets above a garden bed or walkway without proper drainage, that water can pool, freeze, or create a muddy mess that rusts the base of the unit over time.
Always ensure the drain holes under the outdoor chassis are free from leaves and dirt.
Energy Spikes
Your system uses more power when it transitions into and out of a defrost cycle.
If your thermostat is set to an extreme temperature like 26°C, the unit will struggle to hit its target, freeze up faster, and spend half its time defrosting.
Keeping your unit at a steady 18°C to 21°C minimises the frequency of these cycles.
How Long Does a Defrost Cycle Last?
A normal defrost cycle typically lasts anywhere from 5 to 15 minutes.
The exact timing depends on how much ice has accumulated and the current outdoor temperature.
Once the coils are clear, the system will automatically shift back into heating mode.
The indoor fan will start up again, and warm air will return to your rooms.
The Golden Rule
Never turn your system off during a defrost cycle. Let the unit complete its process naturally.
Interrupting it will only prolong the issue, as the ice will remain on the coils.
This forces the unit straight back into defrost mode the moment you switch it back on.
When is it an Actual Fault: Troubleshooting for Perth Homeowners
While frost is normal, a total ice block is not. You should contact a professional service technician if you notice these specific red flags:
- The system stays in defrost mode for more than 20 to 25 minutes without returning to heat.
- Thick, solid ice has completely encased the outdoor unit like a block of wood, and the steam cycle is not melting it.
- The indoor wall controller is actively flashing an error code or showing a red fault light.
- You notice ice forming inside the home on the indoor unit coils, which indicates a serious refrigerant leak or airflow failure.
Understanding these quirks is just one part of mastering your home’s climate control. For a complete look at optimising your system, read our master guide on keeping warm in winter with air conditioning efficiently.