Air conditioning
Air conditioner not turning on?
When an air conditioner will not turn on, the cause is usually outside the unit: flat remote batteries, a tripped circuit breaker or a switch someone turned off in winter. Five minutes of checking sorts out most of them.
5 min read
The short answer
Five checks before you call anyone
Work through these in order. None of them needs a tool or a panel off. Together they clear most of the "dead aircon" calls we get at the start of each summer.
- 1
Swap the remote batteries
The remote is the most common culprit after a winter in a drawer. Fresh batteries, then point it straight at the indoor unit from a metre or two away. Most indoor units beep when they receive a signal.
- 2
Check the mode and the timer
A remote left on a timer or set to heat at 30 degrees on a warm day can look like a system that will not start. Cancel any timer, pick cool and set it a few degrees below the room.
- 3
Look at the switchboard
Find the circuit breaker marked air conditioning. If it has tripped, switch it back on once. If it trips again, leave it off.
- 4
Check the isolator at the outdoor unit
Most outdoor units have a weatherproof switch on the wall beside them. Gardeners, painters and curious kids turn these off more often than you would think.
- 5
Give it five minutes
After a power cut or a reset, many systems hold off starting the compressor for a few minutes. Turn it on, wait and listen for the outdoor fan.
What you see and what it usually means
If the checks above do not bring it back, the way it fails tells a technician a lot.
| What you see | Likely cause |
|---|---|
| No lights, no beep, nothing | No power reaching the indoor unit: breaker, isolator or a wiring fault |
| Lights come on but nothing runs | The system has locked itself out on a fault and is showing a code |
| Indoor fan runs, outdoor unit stays silent | An outdoor fault such as a failed capacitor or contactor |
| Starts, then stops within a minute | A safety cut-out: full drain tray, blocked coil or a sensor fault |
| Ducted controller blank or showing an error | Controller fault or a tripped safety switch in the roof unit |
A table like this narrows it down. It cannot see inside your unit, so treat it as a guide for the phone call rather than a diagnosis.
When to leave it off
Switch the system off at the breaker and call a licensed technician if the breaker trips a second time, you smell burning, the outdoor unit hums without the fan turning or water is pouring from the indoor unit. Each of those points to a fault that gets worse and dearer to fix the longer the system keeps trying to start.
If your system does start but blows warm air, that is a different set of faults. Our guide to an air conditioner that runs but does not cool covers those. Water coming from the indoor unit has its own guide too: why an air conditioner leaks water.
Why so many systems fail to start in October
Most split systems in the Illawarra sit untouched from late autumn until the first hot day. Over that time a drain can dry out and block, a remote battery can go flat and a small fault that developed in May can sit there unnoticed. Then everyone switches on in the same week, finds the problem at once and every technician gets busy.
A spring air conditioning service turns the system on and runs it properly before you need it, so a fault shows up while there is still time to fix it without a hot night in between.
Common questions
- Why won’t my air conditioner turn on after a power outage?
- Most systems wait a few minutes after power returns before the compressor will start, to protect it. Give it five minutes. If it still will not start, check the switchboard, because a surge or a storm can trip the air conditioning circuit on its own.
- Why does my aircon turn on and then turn straight off?
- A system that starts and stops within a minute has usually hit a safety cut-out. Common triggers are a full condensate tray, a blocked outdoor coil or a fault the unit has detected in itself. Check for a flashing light on the indoor unit and note the pattern before you call.
- Should I keep resetting the circuit breaker?
- No. Reset it once. If it trips again, leave it off and call a licensed technician, because a breaker that keeps tripping is protecting you from an electrical fault inside the system.