Split system playing up? Here's what each symptom actually means.

In the great majority of cases, a blocked condensate drain. Your indoor unit condenses moisture out of the room air whenever it cools, and that water collects in a drip tray and drains outside through a small pipe. Over years, dust, algae, mould and sometimes insects or geckos block that line, so the tray overflows into the room — industry service data attributes roughly 85% of internal leak callouts to blocked drains. The next most common cause is clogged filters: restricted airflow makes the coil ice over, and when the ice melts the tray floods. Low refrigerant can cause the same icing, and a unit mounted out of level or a sagging drain line will leak from day one. Start by turning the unit off, cleaning the filters, and checking whether water actually drips from the outdoor end of the drain pipe while it runs. If the pipe is dry while water appears indoors, the line is blocked.

Almost always mould and bacteria growing on the indoor coil and blower wheel. During cooling those components stay damp, dust settles on them, and a biofilm develops that the fan then blows into your room — the sour, damp-sock smell often called dirty sock syndrome. Cleaning the filters helps but frequently is not enough, because the growth sits on the coil fins and inside the blower wheel behind the filters, which is what a professional deep clean addresses. To prevent it recurring, run the unit in fan mode for ten to twenty minutes after long cooling sessions, or use the dry or self-clean function if fitted, so the coil dries before shutdown. Two smells need different treatment: a sharp chemical or sweetish smell can indicate a refrigerant leak and should be checked, and any burning or hot electrical smell means switching the unit off at the switchboard and calling a technician immediately.

Four possibilities, and the first is not a fault. In cold, damp weather the unit periodically runs a defrost cycle, briefly reversing to melt frost off the outdoor coil; during those few minutes it stops delivering heat and the outdoor unit may steam. That is normal. Second, check airflow: dirty indoor filters and an outdoor unit blocked by vegetation, leaf litter or a fence built too close will both cripple heating, because in heating mode the outdoor coil needs airflow to collect heat. Third, the unit may simply lack cold-climate capability — output and efficiency fall as ambient temperature drops, and a cold-climate H2-rated unit holds up far better on genuinely cold nights. Fourth, a real fault such as a failed reversing valve, a refrigerant leak or a failing fan or compressor, which is likely if the unit cools normally but will not heat at all. Before calling anyone, confirm the remote is in heat mode rather than auto and the setpoint is above room temperature.

Ice on the indoor coil during cooling is nearly always caused by restricted airflow or low refrigerant. Dirty filters, a blocked return air path or a failing indoor fan all reduce airflow across the coil, so it runs colder than designed until moisture on it freezes. Low refrigerant produces the same result by dropping the pressure and therefore the coil temperature. Turn the unit off and let it thaw completely before running it again, because operating an iced system risks liquid refrigerant returning to the compressor, which is an expensive failure. Clean the filters, run it again, and if it re-ices then it needs a technician — and if the diagnosis is low refrigerant, insist the leak is found and repaired rather than simply topped up. Frost on the outdoor unit in winter is a different matter entirely: that is expected in cold damp conditions and is exactly what the defrost cycle exists to clear.

Clicking as the unit starts and stops is normal relay and valve operation. A clunk in cold weather is usually the reversing valve switching in or out of a defrost cycle, also normal. Gurgling or bubbling is generally refrigerant moving through the circuit or water in the condensate line, though persistent bubbling combined with poor performance can point to a low charge. Rattling or vibration usually means a loose cover, a loose mounting bracket, or debris caught in the outdoor fan, all cheap to check and fix. The noises that mean stop are grinding or screeching, which suggests a failing fan bearing or compressor, and loud buzzing accompanied by the circuit breaker tripping, which is an electrical fault. In those two cases switch the unit off at the switchboard and call a licensed technician or electrician rather than continuing to run it, because repeated breaker trips are the system reporting a fault rather than a nuisance to reset around.

You can safely clean the indoor filters, which is the single highest-value maintenance task and resolves a large share of complaints. You can clear vegetation and leaf litter from around the outdoor unit and gently hose its fins, avoiding a pressure washer, which bends fins and makes them worse. You can check that the condensate drain is discharging outside and attempt a gentle flush of an accessible drain line. You can check settings, modes and setpoints. Everything else belongs to a technician: anything involving refrigerant is licensed work in Australia requiring an ARCtick refrigerant handling licence, and anything involving the electrical supply, a tripping breaker, burning smells or scorching should be switched off at the switchboard and left to a licensed electrician. Deep cleaning of the indoor coil and blower wheel is also worth paying for rather than attempting, since it involves dismantling parts of the indoor unit and using chemicals near live electrical components.