September 8, 2026 · Cairns Aircon Installers
The system runs for a while, then everything on that circuit goes dead. You walk out to the switchboard, flick the switch back on, and it happens again an hour later. It is tempting to treat the breaker as the problem. It is not. The breaker is the only part of the system doing its job properly.
First, Work Out What Actually Tripped
This matters more than most people realise, because the two devices at your switchboard fail for completely different reasons.
- A circuit breaker trips on too much current. Something is drawing more power than the circuit is rated for, usually because a motor is struggling or there is a short.
- An RCD or safety switch trips on leakage to earth. Current is escaping the circuit somewhere it should not, commonly through moisture or damaged insulation. These are usually the wider switches, often with a test button.
Tell whoever attends which one went. It genuinely narrows the diagnosis by half, and in Cairns an RCD trip has a very likely culprit that we will come to.
1. A Filthy Outdoor Unit
The most common cause we find, and the most preventable. The condenser coil on the outdoor unit sheds heat to the outside air. If it is packed with dust, grass clippings, lawn mower throw, leaf litter or the fine salt and organic film that coats everything near the coast, it cannot shed that heat.
Head pressure climbs, the compressor works harder and harder, current draw rises, and eventually the breaker says no. It usually trips after the system has been running a while and the heat has built, rather than instantly on startup. That timing is a strong clue.
2. A Failing Start Capacitor
The capacitor gives the compressor and fan motors the kick they need to start. As they age they lose capacity, and a weak one means the motor draws very high current while it struggles to get going.
The signature here is different: it trips at the moment of startup, not after an hour. You may also hear a hum or a click from the outdoor unit without the fan spinning up. Capacitors are a consumable component and a routine replacement, but they need to be discharged safely before anyone goes near them.
3. A Seized Or Failing Fan Motor
If the outdoor fan bearing is on its way out, the motor draws more current to turn a shaft that no longer wants to spin. Same result. You will often hear it first, a grinding or a squeal, before it starts tripping anything. Our guide on what the different aircon noises mean goes through this.
4. Moisture And Insulation Breakdown
This is the Cairns special, and it is nearly always an RCD trip rather than a breaker trip. Sustained humidity, driving wet season rain, salt air on the coastal suburbs and UV on exposed cabling all degrade insulation over time. Water finds its way into an outdoor isolator, a junction, or a cable entry that was not sealed properly on install.
Once there is a path to earth, the safety switch does exactly what it is meant to do. The tell is that it trips during or just after heavy rain, or first thing on a very humid morning, and then behaves itself once things dry out. That intermittent pattern is not the system being temperamental. It is a fault that comes and goes with the weather, and it needs finding.
5. A Refrigerant Problem
Both too little and too much refrigerant make the compressor work outside its design envelope and draw more current. Low charge means there is a leak somewhere, because these are sealed systems and refrigerant does not get used up. Overcharge means somebody topped it up rather than finding the leak. Either way it is a licensed job, and it usually shows up alongside poor cooling.
6. The Circuit Is Overloaded Or Shared
Air conditioners should generally be on their own dedicated circuit. We still find systems sharing a circuit with power points, or on a circuit that was adequate for the old unit and is not adequate for what replaced it. It will seem fine until the day everything runs at once.
This shows up a lot in older Cairns homes where an aircon has been added to existing wiring rather than run properly. If the switchboard still has ceramic fuses or no safety switches at all, that is a bigger conversation, and our post on switchboard upgrades and aircon covers what is involved.
What You Can Check Before Calling
- Note which device tripped and whether it was on startup or after running.
- Look at the outdoor unit. Is the coil visibly blocked? Is there anything growing against it? It needs clear air on all sides.
- Check the filters and indoor unit. Restricted airflow indoors makes the whole system work harder.
- Note whether it correlates with rain. Genuinely useful information.
Then stop. Everything past this point is inside an enclosure with capacitors that hold a dangerous charge even with the power off, and connections that carry enough current to kill you. This is not a job to have a go at.
Get It Diagnosed
A tripping system is telling you something is wrong, and the fault will not improve on its own. See our aircon repairs page, or get in touch and tell us which switch went and when. Leave it off until then.