Owner Guide
How to Prepare Your Air Conditioner for Winter Heating
If you rely on reverse cycle heating, it pays to prepare your air conditioner for winter before the first frosty morning. A system that cooled happily all summer may still struggle once you switch it to heat. This guide explains the checks worth doing in autumn, the normal winter behaviours that worry owners and how to stay warm without overspending.
Why Bother
Why Does Winter Heating Need Its Own Preparation?
Heating mode asks a reverse cycle system to work in a different way. The reversing valve switches the flow of refrigerant, the outdoor coil becomes the cold side and the unit must cope with frost. Parts that sat quietly through summer suddenly get a workout.
Moreover, summer leaves its mark. Filters fill with dust and pollen during months of cooling. Leaves pile up around the outdoor unit in autumn. Drain lines can carry a summer’s worth of slime. None of this stops the system in a heartbeat, yet together these issues reduce heating output.
A little attention in April or May means the unit is ready when the cold arrives. In Melbourne, Adelaide and the colder parts of Sydney, that can be surprisingly early. Even in Brisbane and Perth, chilly mornings make reliable heating welcome.
Warm From Day One
A checked system heats properly the first time you need it, rather than after a service call.
Efficient Heating
Clean filters and a clear outdoor coil let the system deliver more warmth for each unit of power.
Fewer Surprises
Knowing what defrost looks like stops a normal cycle from feeling like a breakdown.
Autumn Routine
What Steps Prepare an Air Conditioner for Winter?
The routine below takes under an hour for many homes. Choose a dry day in autumn, ideally before overnight temperatures drop sharply. Follow each step in order for the best result.
Isolate the Power
Switch off at the remote or controller first, then at the isolator or circuit breaker so the fan cannot start unexpectedly.Clean Every Filter
Vacuum and gently wash the indoor filters, or the ducted return air filter. Dry them completely before refitting.Clear Autumn Debris
Remove fallen leaves, twigs and grass from around and under the outdoor unit, keeping your hands clear of the fan.Check Drainage Outdoors
Make sure melt water from defrost cycles can drain away freely and will not pool on paths or freeze where people walk.Restore Power and Select Heat
Turn the power back on, choose Heat mode and set a temperature a few degrees above the room temperature.Allow the Warm Up Delay
Give the unit several minutes. Many models hold the indoor fan back until the coil is warm enough to avoid a cold draught.Run a Full Test
Let it heat for at least twenty to thirty minutes, checking for steady warm air and no unusual noises or smells.
Multi head systems need one extra step. Because every indoor unit shares a single outdoor unit, set them all to Heat before testing. A head left on Cool can conflict with the others and may sit on standby, which looks like a fault but simply reflects a mode clash. Test each room in turn once all heads match.
Also take a moment to note anything unusual during the test, such as a new rattle, a slow louvre or a display that flickers. Writing it down, with the date and the brand and model of the unit, makes any later booking quicker and helps the technician find the cause sooner.
Our guide on how to clean air conditioner filters covers the filter step in detail. The sections below explain what to watch for during the test.
Normal Behaviour
Why Does My Air Conditioner Stop Heating for a While in Winter?
This is the question we hear most each winter. The answer, in most cases, is defrost. It is a normal and necessary part of reverse cycle heating, not a sign of failure.
Here is why it happens. In heating mode, the outdoor coil runs colder than the outside air so it can absorb warmth. On cold, damp days, moisture in the air freezes onto that coil as frost. Over time, the frost blocks airflow and cuts heating output. So the unit pauses, reverses briefly and warms the outdoor coil to melt the ice.
What You Notice Indoors
The indoor fan slows or stops, warm air pauses and an indicator light may change or flash. Some displays show a defrost symbol.
What You Notice Outdoors
The outdoor fan may stop, you may hear a whoosh as the valve switches and steam may rise from the unit. Water drips from the base.
How Long It Lasts
Defrost typically runs for a few minutes, then heating resumes automatically. Frequency depends on temperature and humidity.
Defrost becomes a concern when ice builds up and does not clear, or when heating rarely resumes. Our page on ice on the outdoor unit explains the warning signs. If the unit blows cold air for long periods, see blowing cold air on heat.
Outdoor Unit
How Should You Look After the Outdoor Unit in Winter?
In winter, the outdoor unit faces cold, rain, frost and sometimes wind blown debris. It is built for outdoor conditions, yet a few simple steps help it work well through the cold months.
Above all, airflow and drainage matter. The unit needs air moving freely through its coil to collect warmth, and it needs somewhere for defrost water to go. If water cannot drain, it may refreeze around the base and gradually build up ice.
Do This
- Keep leaves and garden waste clear of the coil
- Leave space around the unit for air to move
- Check that defrost water drains away from paths
- Make sure the unit stays level on its base or brackets
- Look for damaged pipe insulation after storms
Avoid This
- Covering the unit while it is in use for heating
- Chipping ice off the coil with tools
- Pouring boiling water over a frozen unit
- Stacking firewood or bins against the casing
- Ignoring a fan that will not spin
Covers deserve a special mention. A fully covered outdoor unit cannot breathe, so it cannot heat. If you use a cover at all, it should only go on when the system is not being used, and it must come off completely before you run the unit.
Settings
Which Settings Give the Best Winter Heating Results?
Good settings make a big difference to winter comfort and cost. Warm air naturally rises, so heat collects near the ceiling unless you push it down. Equally, very high set points cost more without making you feel much warmer.
- Choose Heat mode rather than Auto on cold days for predictable results.
- Set a moderate temperature, roughly 18 to 20 degrees for living areas.
- Aim the louvres downward so warm air reaches the floor.
- Use Auto fan, which starts strong and eases off as the room warms.
- Close doors to rooms you are not heating.
- Set a timer to warm bedrooms shortly before bed, rather than all evening.
- Update app schedules for shorter days and earlier evenings.
Our guides on the best air conditioner temperature settings and air conditioner modes explained go into more depth. If your unit is connected, see the WiFi and app control guide for scheduling tips.
Ducted Heating
What Should Ducted System Owners Check Before Winter?
Ducted reverse cycle systems need the same basic care, plus a few extra checks. Begin with the return air filter behind the hallway grille. Then test the system in Heat mode with each zone in turn.
Warm air from ceiling outlets tends to stay high in the room. That is why ducted heating can feel less even than cooling. Some homes benefit from floor or low wall returns, but that is a design matter for a professional. For now, simply note any rooms that stay cold.
Return Filter
A clean return filter lets the system move its full volume of air, which matters for heating performance.
Zone Test
Open each zone individually and confirm warm air reaches every outlet in that area.
Controller Check
Look for warnings on the wall controller and confirm the clock and schedules are correct.
If a zone stays cold, our pages on ducted zone not working and one room not cooling apply equally to heating, since the same dampers and ducts are involved.
Warning Signs
What Heating Problems Should Make You Call a Technician?
Some winter behaviours are normal, while others point to a fault. The difference often lies in how long the symptom lasts and whether it clears on its own.
Usually Normal
- A short delay before warm air starts
- Brief pauses for defrost with steam outdoors
- Water dripping from the outdoor unit base
- A soft click or whoosh when modes change
- Slower warm up on very cold mornings
Needs Attention
- Cold air for long periods in Heat mode
- Thick ice that does not clear after defrost
- Water leaking from the indoor unit in winter
- Grinding, screeching or loud banging noises
- A flashing light or error code that returns
- Repeated tripping of the circuit breaker
Brand specific troubleshooting pages can help narrow down the cause. See Daikin not heating, Mitsubishi not heating, Panasonic not heating, Samsung not heating, Fujitsu not heating and LG not heating. If a code is showing, the error code library covers the major brands, including Fujitsu error codes and Panasonic error codes.
Running Costs
How Can You Keep Winter Heating Costs Down?
Reverse cycle heating is one of the more efficient ways to warm a home with electricity. Still, winter bills can climb when the system runs for long hours. Small changes to the house and to your habits help keep costs in check.
Start by keeping heat in. A warm room loses heat through windows, gaps around doors and an uninsulated ceiling. Each one you address means the air conditioner runs less to hold the same temperature.
Heavy Curtains
Close them at dusk to trap warmth. Curtains that reach the floor and cover the frame work best.
Draught Stoppers
Door snakes and weather seals stop cold air sneaking in under doors and around frames.
Let the Sun In
Open north facing curtains on sunny winter days to collect free warmth, then close them in the late afternoon.
Heat Only Used Rooms
Close doors and zones to unused areas so the system concentrates on where people are.
Dress Warmly
A jumper and slippers let you feel comfortable at a lower set point without any extra cost.
Maintain the System
Clean filters and a clear outdoor unit keep heating output high through the season.
For more ideas, read how to reduce air conditioner running costs. The running costs calculator lets you estimate what your system costs to run over a winter.
Professional Service
Is an Autumn Service Worth Booking?
For many households, yes. Owner checks cover the basics, but a professional service reaches the parts that matter most for heating. A technician can clean the indoor coil and fan, check the reversing valve operates correctly and inspect the outdoor coil and its defrost function.
They will also check electrical connections and measure how well the system performs. If refrigerant levels need attention, that work must be done by an ARCtick licensed technician. The technicians we send hold the licences their work requires.
Autumn is a quieter time for many technicians, so booking is often easier than in summer. For guidance on how often to service, see how often you should service your AC. If you are noticing small changes in performance, our article on signs your air conditioner needs repair may help you decide.
Good to Know
Is There Anything Else Owners Should Know About Winter Heating?
A few final points round out winter readiness. They cover safety, damp homes and what to do when the power goes out on a cold night.
Open more detail
Damp homes benefit from a mix of heating and moisture control. Condensation on windows and mould in corners are common in winter, especially in older homes. Dry mode on mild, damp days, combined with good ventilation, helps reduce moisture without overheating the house.
If the power fails on a cold night, switch the unit off at the remote. When power returns, wait a few minutes before turning it back on. This avoids the system restarting under heavy load. If it will not restart, see our page on not working after a power outage, and our guide on resetting common air conditioning faults yourself.
Finally, never use the outdoor unit as a shelf for drying clothes or as a spot to store heaters and gas bottles. Keep the area around it clear and safe. If you notice a burning smell from either unit, switch it off at the breaker and book a technician.
Questions
Frequently Asked Questions
Why Does Steam Come Out of My Outdoor Unit in Winter?
That is the defrost cycle melting frost from the outdoor coil. The warm coil turns some of the melt water into vapour. It is normal and stops once defrost finishes.
How Long Should It Take for Warm Air to Come Out?
Usually a few minutes after selecting Heat. Many units deliberately hold the fan back until the coil is warm. Longer delays on very cold mornings are also common.
Is It Safe to Run Reverse Cycle Heating Overnight?
Yes, these systems are designed for long running. Many owners use a sleep function or an off timer to avoid overheating the bedroom as the night goes on.
Should I Use Auto Mode in Winter?
On cold days, Heat mode usually gives more predictable comfort. Auto can switch to cooling if the room overshoots, which is rarely what you want in winter.
Why Is Ice Building Up on My Outdoor Unit?
Light frost that clears during defrost is normal. Thick ice that stays, or ice building up at the base, can point to a drainage or defrost fault and should be checked.
Can I Prepare My Air Conditioner for Winter Myself?
The owner checks in this guide are safe for most people. Internal cleaning, electrical work and refrigerant handling must be done by a licensed technician.
Does Winter Heating Wear Out the System Faster?
Reverse cycle systems are built for both heating and cooling. Regular maintenance and sensible settings matter far more for longevity than the season of use.
Stay Warm
Where Can You Book Winter Heating Help Across Australia?
If your test run revealed a problem, or you would rather have a professional check the system before winter, we can book a licensed technician in your city.
Choose your city: Sydney air conditioner repairs, Melbourne air conditioner repairs, Brisbane air conditioner repairs, Perth air conditioner repairs and Adelaide air conditioner repairs. Start with self checks on the troubleshooting hub, or visit our main air conditioning service Australia page.
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Heating Not Working as It Should?
Call us and we will book a licensed technician to get your system ready for winter.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles