Short answer
A unit that runs but does not cool usually comes down to one of four things: restricted airflow from dirty filters or coils, low refrigerant caused by a leak, a failed electrical component such as a capacitor or fan motor, or a control fault. They present almost identically, which is why the cause has to be diagnosed rather than guessed. A few checks you can safely do yourself will sometimes solve it, and will otherwise save time when you call.
What you can safely check first
These are worth ruling out before booking anything:
- Confirm the mode is set to cool, not fan or dry, and the set temperature is below room temperature
- Check and clean the filters — restricted airflow is the single most common cause
- Check the outdoor unit is running and not blocked by plants, bins or stored items
- Check whether any breaker or isolator has tripped
- Note any error code shown on the controller
- Check whether all rooms are affected or only one
Restricted airflow
Dirty filters, a fouled indoor coil or a blocked outdoor unit all reduce the system's ability to move heat.
This is the most common cause and the one most often fixed by a clean. In Brisbane's humidity a coil can foul enough to visibly reduce output within a couple of seasons.
Low refrigerant
Refrigerant is not consumed in normal operation. A system that is low has lost it somewhere, which means there is a leak.
This matters because simply topping the system up puts you back in the same position within months. The leak needs to be traced and repaired, and handling refrigerant requires ARCtick authorisation.
Electrical component failure
A failed capacitor is a common culprit: the fan may run while the compressor does not, so air moves but never gets cold.
Contactors, fan motors and supply faults produce similar symptoms. These are electrical faults on an air-conditioning system, which is where holding both licences avoids a job being split between two trades.
When to turn it off
If you can see ice forming on the pipework or the indoor coil, switch the system off. Running it iced up risks liquid returning to the compressor, which is an expensive failure.
Turn it off and call if there is a burning or electrical smell, or if it trips the breaker when it starts.
What happens on a call-out
Diagnosis comes first: symptom and history, then testing to separate airflow, refrigerant, electrical and control causes.
Once the actual fault is known, the repair is quoted. Nothing gets replaced speculatively, because fitting parts hopefully is the most expensive route to an answer.
General information only. Do not open equipment or attempt refrigerant work yourself; it requires ARCtick authorisation. Hoff works weekdays and does not offer a 24-hour emergency service.