Why is my ducted air conditioning not working?

First identify how much of the system has stopped

The most useful first distinction is whether the fault affects the whole installation, several zones or one room.

• Nothing responds: note whether the wall controller is blank, displays a code or still accepts commands. The supply, controller, indoor equipment or system controls may need testing.
• The fan runs but every outlet feels warm: check the selected mode and set point. The outdoor equipment, controls, electrical components or refrigerant circuit may then require diagnosis.
• One zone does not respond: the zone command, motor, damper, wiring or duct serving that area may be involved.
• One room has weak airflow: outlet position, a restricted or damaged duct, balancing, door/return-air path or room heat load may need to be separated.
• The system starts and stops: record what actually stops (the display, indoor fan, outdoor unit or only the cooling) and how long it runs.

These observations guide testing; they do not confirm the failed part.

Checks that do not require roof-space access

Confirm the controller is in the intended mode, the target temperature calls for heating or cooling, timers are inactive and the expected zones are selected. Check that the return-air grille is unobstructed and clean only the user-accessible filter in accordance with the manufacturer instructions.

Note whether air temperature and volume differ between rooms. Do not climb into a hot, restricted or unfamiliar roof space, stand on ceiling linings, move insulation or open the indoor fan-coil to investigate.

If a code or flashing pattern appears, photograph it before any manual-prescribed reset and read what an air-conditioner error code can tell you.

Ducted faults can sit in different parts of the installation

A ducted system combines the air-conditioning plant with an air-delivery and control system. Diagnosis may need to consider:

• the wall controller, sensors and zone-control platform;
• the indoor fan coil and accessible return-air filter;
• the outdoor unit, electrical supply and refrigerant circuit;
• zone motors and whether commanded dampers actually move;
• flexible ducts, plenums and connections for crushing, disconnection or leakage; and
• outlet airflow, return-air paths and room-specific heat load.

A clean cannot correct a failed zone motor, disconnected duct or electrical fault. Equally, replacing the outdoor unit will not repair poor air delivery if the ducts, dampers or return-air arrangement remain defective.

What a ducted diagnosis should prove

Testing should follow the reported pattern rather than focus on only one component. Depending on the fault and access, it can include controller and error-history checks, indoor and outdoor response, temperature and airflow observations at multiple outlets, zone commands, visible duct and damper condition, drainage and electrical or refrigerant-circuit tests.

The written finding should separate:

• plant and equipment faults;
• controller or zone-control faults;
• duct and air-delivery observations;
• building load or design limitations; and
• the work proposed now, further access or testing required, and items excluded.

Roof access can change the first-visit outcome

The indoor unit, zone motors and much of the ductwork may be concealed. Safe access can depend on the roof entry, ceiling structure, insulation, temperature, equipment position and clear working space. Photos or plans can help preparation but cannot guarantee that every concealed component will be accessible on the first visit.

The initial scope should state whether controller review, roof-space inspection, zone checks, multiple outlet readings and outdoor-unit assessment are included. Parts availability, intermittent faults and access can lead to a repair quote or return visit rather than an immediate repair.

Repair, service or replacement?

Use planned servicing and cleaning for routine filter, coil, fan and drain care without a discrete fault. Sudden loss, a dead zone, error code, water, breaker operation or failure to cool requires fault diagnosis.

Repair can remain sensible when the fault is isolated and the wider plant, ducts, controls and electrical installation remain serviceable. If replacement is being considered, the assessment should state what happens to the existing ducts, return air, zoning, controller and electrical supply rather than assuming they can all be reused. See should I repair or replace my air conditioner? and the ducted installation guide for the separate design decision.

What to send with the enquiry

Provide the suburb, controller and equipment models, approximate age, number of zones, rooms affected, exact operating pattern and any code, water, noise, smell or breaker history. Include safe photographs of the controller, return-air grille, model labels and roof-access point without opening equipment or entering the roof space.