If your air conditioner is not turning on, check four things first: power at the switchboard, the isolator switch near the outdoor unit, the remote batteries, and whether a timer or schedule is set. If all four are fine and a light on the indoor unit is flashing, the unit has stopped itself and stored a fault code. That code tells a technician where to look.
Most no-start calls turn out to be something simple. The checks below take under ten minutes and need no tools. After that, the table shows the causes that do need a technician, so you know what you are dealing with before you book.
First, what kind of “not turning on” is it?
- Completely dead: no beep, no lights, no display. Start with power and the remote.
- Beeps or lights up, then nothing: the unit is receiving the command but a protection or fault is stopping it. Look for a flashing lamp.
- Indoor fan runs but no cold or hot air: the indoor unit is on and the outdoor unit is not. That is a different fault; see our guide to an air conditioner not cooling.
Quick checks you can do safely
- Remote. Replace the batteries. Point a phone camera at the remote’s tip and press a button; if you see no flicker on the screen, the remote is not sending.
- Mode and timer. Check the remote is not on a timer, sleep or weekly schedule, and that the mode matches what you want (snowflake for cool, sun for heat).
- Circuit breaker. At the switchboard, look for a tripped breaker marked air conditioner or A/C. Reset it once. If it trips again, leave it off and call a technician.
- Isolator switch. The outdoor unit has a weatherproof switch on the wall beside it. Make sure it is on.
- Power reset. Turn the unit off at the isolator or breaker for five minutes, then back on. This clears many temporary lockouts after a power cut or storm.
- Manual button. Most indoor units have a small on/off button under the front panel. If the unit starts from that button but not the remote, the fault is the remote or its receiver.
If a breaker trips repeatedly, you smell burning, or the unit buzzes without starting, switch it off and leave it off. Those point to an electrical fault.
Causes and what each one needs
| Cause | What you’ll notice | DIY or technician |
|---|---|---|
| Flat remote batteries or a faulty remote | No beep; the manual button works | DIY: batteries, or a replacement remote |
| Timer, sleep or schedule setting | Starts at odd times or not at all | DIY: clear the timer |
| Tripped breaker or isolator off | Completely dead | DIY once; technician if it trips again |
| Protection lockout after a power surge | Flashing lamp; clears after a power reset | DIY reset; technician if it returns |
| Failed control board (PCB) | Dead or erratic even with power present | Technician |
| Failed capacitor or fan motor in the outdoor unit | Indoor unit on, outdoor unit hums or stays still | Technician |
| Sensor fault or communication error | A specific error code on the display or lamps | Technician |
| Condensate pump or float switch fault (some ducted and cassette units) | Stops to prevent a water overflow | Technician |
What a flashing light means
A flashing operation or timer lamp means the unit has detected a fault and switched itself off to protect a component. The pattern, or the code the remote can display, points to the part involved. A steady filter lamp is only a cleaning reminder.
Write down the code before you reset anything. Our air conditioner symbols guide covers the lights, and the brand error-code guides below list the codes.
After a power outage or storm
Many systems will not restart straight after a blackout. Some wait a few minutes to protect the compressor, and some need to be turned on again from the remote. If the unit is still dead after a five-minute power reset, a surge may have damaged the control board, which is a job for a technician.
Brand guides
| Brand | Not turning on | Error codes and lights |
|---|---|---|
| Daikin | Daikin not turning on | Daikin error codes |
| Mitsubishi Electric | Mitsubishi not turning on | Mitsubishi symbols |
| Fujitsu | Fujitsu not turning on | Fujitsu error codes |
| Panasonic | Panasonic not turning on | Symbols guide |
| Samsung | Samsung not working | Samsung error codes |
| LG | General troubleshooting | LG symbols |
When to call a technician
Call once the quick checks are done and the unit still will not start, if a breaker keeps tripping, or if the same error code keeps coming back. Tell us the brand, the model if you have it, and any code on the display; it helps the technician bring the right parts. You can book online or see what our air conditioner service covers.
For every other symptom, start from our air conditioner troubleshooting hub.
For general advice on staying safe around electrical appliances at home, see Energy Safe Victoria.
Guides for your brand or problem
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles