QualifiedHigh risk

Split-system air-con not running at all

A split-system (head unit + outdoor condenser) is completely dead — no response from the remote/controller — pointing at supply, isolator, controller, or the indoor PCB.

Start fault-finding

Safety first

Isolate at the dedicated isolator and prove dead before working. Refrigeration/gas work is restricted to licensed refrigeration techs — this covers the electrical side only.

Isolate, lock out / tag out, and prove dead before working unless a live test is specifically required, authorised, and carried out under proper supervision. Always follow local regulations, your site procedures, and the equipment manufacturer's documentation.

Full detail — causes, the why, and common mistakes.

Likely causes

Ranked from most to least likely.

  1. 1

    No supply / isolator off / tripped

    Most likely

    The dedicated aircon isolator is off, or the circuit has tripped.

  2. 2

    Remote/controller fault or batteries

    #2

    A dead remote or wall controller means no run command.

  3. 3

    Indoor unit PCB / control fault

    #3

    The indoor control board has failed.

  4. 4

    Indoor-outdoor interconnect fault

    Least likely

    The interconnecting control/power wiring between units is faulty.

Reports are saved on this device to reflect what you actually find.

Testing sequence

Work through one test at a time. Expected reading and what each result means.

Test 1 of 3
1

Check the dedicated isolator and circuit, and confirm supply at the indoor unit.

Expected reading

Isolator on, circuit healthy, supply present.

If it passes

Powered — check the controller/remote and indoor PCB.

If it fails

Isolator off / tripped / no supply — restore (find why if tripped).

Often leads toAir-con tripping the powerAir-con runs but isn't cooling (electrical checks)
View all expected readings at once
1. Check the dedicated isolator and circuit, and confirm supply at the indoor unit.
Isolator on, circuit healthy, supply present.
2. Check the remote/controller (batteries, response) and try a basic run command.
Controller responds and commands a run.
3. Isolate and check the indoor-outdoor interconnect wiring and the indoor PCB per the unit docs.
Sound interconnect and a responsive PCB.

Fault-finding flowchart

The same logic as a decision tree.

  1. 1
    start

    Split system dead

    → step 2
  2. 2
    decision

    Is the isolator on, circuit healthy, supply present?

    Yes→ step 3No→ step 4
  3. 3
    decision

    Does the controller/remote respond and command a run?

    Yes→ step 5No→ step 6
  4. 4
    result

    Restore isolator/circuit/supply.

  5. 5
    result

    Suspect interconnect or indoor PCB — rectify / qualified service.

  6. 6
    result

    Dead remote/controller — batteries / rectify controller.

Common mistakes apprentices make

  • Not checking the dedicated isolator (often a separate switch).
  • Overlooking a dead remote/controller.
  • Attempting refrigeration work without a refrigeration licence.
  • Working without isolating at the unit.

When to stop & escalate

Electrical supply/isolator/controller work is licensed electrical; refrigeration faults and gas work need a licensed refrigeration technician. PCB faults usually need the manufacturer/qualified service.

If you're past your competence, authorisation, or the safe limits of the job — stop and hand it on. There's no fault worth getting hurt over.

Related faults

HVAC & air-con

Air-con tripping the power

An air-con unit trips its breaker or safety switch — on start, when the compressor kicks in, or randomly — pointing at the compressor, an earth fault, or the supply/protection.

5 causes3 test steps
AdvancedHigh risk
HVAC & air-con

Air-con runs but isn't cooling (electrical checks)

The unit runs (fan blows) but doesn't cool — from an electrical standpoint, checking whether the compressor/outdoor unit is actually being commanded and powered before handing to refrigeration.

4 causes2 test steps
QualifiedMedium risk
HVAC & air-con

Ducted air-con system has no power / won't start

A ducted system (roof/cupboard fan unit + zones/controller) is dead or won't start — pointing at the dedicated supply/isolator, the controller, zone motors, or the unit's PCB.

4 causes3 test steps
QualifiedHigh risk

Learn the theory

How the gear and circuits behind this fault actually work.

Principle

How HVAC control works (electrical view)

A thermostat/controller calls for heating or cooling; the electrical side energises the unit — refrigerant is separate.