If your air conditioner is not working, start with the symptom. Most air conditioner faults fall into a handful of groups, and each has checks you can do safely in a few minutes. Find your symptom in the table below. It lists the usual causes, what to check first, and the full guide. If you see a flashing light or an error code, write it down before you reset anything.
Match your symptom
| Symptom | Usual causes | Check first | Full guide |
|---|---|---|---|
| Won’t turn on at all | Remote, breaker, isolator, timer, control board | Batteries, breaker, isolator switch | Not turning on |
| Runs but doesn’t cool | Mode, filters, outdoor unit, low gas | Mode on cool, clean filters | Not cooling |
| Won’t heat | Mode, defrost cycle, filters, reversing valve | Mode on heat; wait out defrost | Not heating |
| Water leaking inside | Blocked drain, frozen coil, unit not level | Outside drain dripping? | Leaking water |
| Ice on the coil or pipes | Airflow, low gas, cooling on cold nights | Fan mode to thaw; clean filters | Frozen |
| Keeps turning off | Timers, filters, protection, breaker | Clear timers; note error codes | Keeps turning off |
| Outdoor unit not running | Isolator, capacitor, contactor, fan motor | Isolator and breaker | Outdoor unit not running |
| Indoor fan not working | Fan motor, capacitor, control board | Fan speed setting | Fan not working |
| Strange noise | Loose panels, debris, electrical parts, bearings | Clear the outdoor unit | Making noise |
| Bad smell | Mould on the coil, drain, electrical burning | Burning smell: switch off | Smells |
| Remote not responding | Batteries, key lock, receiver | New batteries; camera test | Remote not working |
| Flashing light or error code | Stored fault | Write down the code | Symbols and lights |
Five checks to do before anything else
- Power: check the circuit breaker at the switchboard and the isolator switch beside the outdoor unit.
- Remote: fresh batteries, correct mode, and no timer or schedule set.
- Filters: slide them out; clean them if they are grey.
- Outdoor unit: clear leaves and clutter, and check the fan spins when the system runs.
- Power reset: switch off at the isolator for five minutes, then back on. Reset once only.
When it isn’t safe to DIY
- A breaker that trips again after one reset
- A burning smell, smoke, sparking or scorch marks
- Water near power points or running inside the wall
- Anything involving refrigerant or opening either unit. Refrigerant work must be done by an ARCtick-licensed technician.
Brand-specific guides
| Brand | Guides |
|---|---|
| Daikin | Not turning on, not cooling, error codes, flashing green light |
| Mitsubishi Electric | Not turning on, not cooling, symbols |
| Fujitsu | Not turning on, leaking water, error codes, reset |
| Panasonic | Not turning on, leaking water |
| Samsung | Common problems, error codes |
| LG | Symbols |
Need a technician?
If the checks don’t fix it, book online and tell us the brand, the symptom and any error code. For resets you can safely try yourself, see how to reset common air conditioning faults.
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