When your aircon stops cooling properly, most homeowners assume the unit is “just old” or “needs gas.”

But one of the most common problems in Brisbane homes is this:

The indoor unit is running
but the outdoor unit is NOT

And here’s the truth:
When the outdoor unit stops running, it often isn’t an aircon issue first.
It’s often an electrical issue, and ignoring it can lead to:

• repeated tripping

• major damage to the system

• expensive repairs

• or safety risks if a fault is involved

Let’s break down the most common electrical reasons your outdoor unit stops working.

1. The Outdoor Unit Has Lost Power (Isolator or Circuit Issue)

Outdoor units usually have their own power supply and isolator.

If the isolator is off, faulty, or damaged, the outdoor unit will not start at all.

Common signs:

• indoor unit blows air but never cools

• outdoor fan is silent

• outdoor unit doesn’t vibrate or hum

• no lights or response from the unit

A licensed electrician can confirm whether the outdoor supply is actually live.

2. The Circuit Breaker Keeps Tripping

Your outdoor unit draws a heavy load especially during Brisbane summer afternoons.

If the breaker is weak, worn, or overloaded, it may trip to prevent overheating.

Causes include:

• breaker too sensitive

• old switchboard

• circuit overload

• wiring strain

• aircon drawing too much startup current

If the breaker trips repeatedly, it’s not something to reset over and over.

3. A Failing Capacitor Causes the Outdoor Unit to Stall

Capacitors are electrical components that help the compressor and fan motor start.

When they fail, the outdoor unit may:

• try to start then stop

• hum but not run

• shut off after a few seconds
  
  

This is one of the most common causes of outdoor unit failure and is often triggered faster by heat.

4. Loose Wiring or Burnt Terminals (Common After Years of Heat)

Brisbane heat expands materials, and over time, terminals can loosen.

Loose connections cause:

• arcing

• overheating

• power loss to the unit

• sudden shutdowns

Warning signs:

• burning smell near the outdoor unit

• buzzing sounds

• random shutdowns during hot afternoons

• melted or discoloured wiring covers

This is a real fire risk when ignored.

5. The Safety Switch (RCD) is Tripping Due to Leakage Current

Outdoor units are exposed to weather and moisture.

If there’s a fault on earth, the safety switch can trip.

Common causes:

• moisture inside wiring

• cracked insulation

• damaged cables

• failed compressor windings

If your RCD trips only when the aircon runs, that’s a strong sign there’s an electrical leakage fault.

6. The Outdoor Unit Is Overheating and Going Into Protection Mode

Outdoor units protect themselves when electrical conditions are unsafe.

This can happen due to:

• overheating from poor airflow

• extreme Brisbane heat

• blocked coils

• failing fan motor

• electrical strain

When protection mode activates, the unit may stop completely and only restart later.

7. Voltage Problems (Brownouts / Fluctuations)

On extreme heat days, Brisbane homes can experience voltage drops due to high demand.

Outdoor units are sensitive to voltage changes.

If voltage dips too low, the compressor may:

• fail to start

• stall mid-cycle

• shut down to protect itself

This often looks like a “random fault” but it’s an electrical supply issue.

8. The Contactor or Relay Has Failed

The contactor is like a switch that tells the outdoor unit when to start.

If the contactor fails, the outdoor unit won’t activate even if the indoor unit is calling for cooling.

Signs include:

• indoor unit running normally

• outdoor unit completely silent

• no response when cooling is selected

This needs professional testing because it involves live power.

When It’s a Safety Emergency (Call Immediately)

If you notice any of these, stop using the system and get it checked:

• burning smell

• sparking sounds

• repeated breaker trips

• outdoor wiring looks melted

• outdoor unit feels extremely hot

• buzzing near the switchboard when the unit starts

These signs can indicate wiring faults or overheating components.

Final Word: Don’t Keep Resetting It. Find the Cause

If your outdoor unit keeps stopping, it’s not something to ignore.

The earlier the electrical cause is diagnosed, the lower the chance of:

• full system failure

• blown components

• expensive compressor damage

• or electrical hazards

👉 Need an aircon electrical inspection in Brisbane?
Contact Exclusive Electrical & Air to have the outdoor unit power supply, wiring, and protection systems checked safely by a licensed electrician.