Written by Oliver Hastings on 9 November 2026
Why is my ducted air conditioner running but not cooling?
If your ducted air conditioner is not cooling, a failed run capacitor on the condenser fan motor is a common cause. During a scheduled service in Windsor Gardens on 4 November 2026, our technician found that the condenser fan run capacitor had failed. We replaced it with a matched 5 uf capacitor on the same visit, and the condenser fan was restored to operation.
The Job In Brief
- System: Hitachi ducted air conditioning
- Suburb: Windsor Gardens, Adelaide SA
- Booked as: Ducted air conditioning service
- Fault found: Failed run capacitor on the condenser fan motor
- Part replaced: 5 uf run capacitor
- Also found: Open air bender in the duct system (quoted for further work)
- Repair price guide: $300 to $600 inc GST (correct at 4 November 2026)
- Outcome: Work completed; further work quoted
The Fault
The booking was for a routine ducted air conditioning service on a Hitachi system. During that service, our technician found the condenser fan run capacitor had failed.
The run capacitor is a small electrical component connected to the condenser fan motor in the outdoor unit. Its job is to maintain the electrical phase shift that keeps the motor turning smoothly under continuous load. When the capacitor fails, the motor loses that support and can no longer maintain rotation. Without a spinning condenser fan, the outdoor unit cannot push air across the refrigerant coil to reject heat, and the system’s ability to cool deteriorates.
A degrading capacitor does not always fail suddenly. As capacitance falls below the motor’s rated value, the motor can produce sluggish startups, run at reduced speed, or draw more current than normal. Those early signs can be easy to miss, which is why a scheduled service is an opportunity to check the electrical components in both the indoor and outdoor units, not just the filters.
What We Tested
Our technician attended the site and carried out the ducted service. As part of that work, the condenser unit was inspected and the run capacitor on the fan motor was identified as faulty. A quote to replace it was raised and approved on the same visit.
During the service, the duct system was also inspected. An open air bender was found and quoted as a separate item for future rectification. No further defects were recorded in the service notes.
Run capacitors carry a rated capacitance measured in microfarads (uf). According to the Wikipedia article on motor capacitors, capacitance naturally declines with years of use, and a faulty capacitor often shows physical signs such as swelling or bulging. When capacitance drops below the motor’s requirement, the motor’s windings draw excessive current, generating heat that shortens the motor’s working life. Catching a failed capacitor before the motor itself is damaged avoids a more costly repair.
How We Fixed It
We replaced the failed component with a new 5 uf run capacitor matched to the condenser fan motor’s specification. The service and capacitor replacement were both completed on the same visit.
The price guide for a condenser fan run capacitor replacement on a ducted system is $200 to $300 inc GST during a service, correct at 4 November 2026. That is a guide only. A standard ducted service is $290 inc GST. For an accurate quote on your system, call 08 8296 7888 or use the contact page.
Capacitor replacement is electrical work carried out by a licensed air conditioning technician. Where fault diagnosis also involves the refrigerant circuit, the technician must hold a current Refrigerant Handling Licence under the ARCtick scheme. Homeowners can verify any technician’s licence status at lookforthetick.com.au before work begins.
| Stage | What we did | What it showed |
|---|---|---|
| Service and inspection | Attended site and serviced the Hitachi ducted system | Condenser fan run capacitor found to have failed |
| Repair | Replaced the 5 uf run capacitor on the condenser fan motor | Condenser fan restored to operation |
| Further findings | Inspected duct system during the service | Open air bender found and quoted for future rectification |
Key Takeaways
- Warning signs at the outdoor unit: If the outdoor unit is running and humming but the fan blade is not spinning, or the system runs but barely cools the house, a capacitor fault is worth investigating before the problem reaches the fan motor.
- Warning signs indoors: Sluggish cooling, warm air from the vents, or a system that runs for long periods without reaching the set temperature can all point to a condenser fan that is not operating at full capacity.
- What you can safely check yourself: Confirm the isolator switch at the outdoor unit is on, check that the circuit breaker has not tripped, and clean the return air filter inside. These steps cost nothing and rule out the simple causes before calling a technician.
- When to stop and call a licensed technician: Do not open the electrical compartment of the outdoor unit. Run capacitors hold a stored charge even after the power is switched off, and they require safe discharge before handling. This work must be done by a qualified technician.
- An annual service is the most reliable early warning: A scheduled service gives a technician the chance to check run capacitors and other electrical components before they fail completely. Replacing a marginal capacitor costs considerably less than replacing a fan motor that has burned out as a result.
The Resolution
The ducted service and run capacitor replacement were completed on 4 November 2026. The outcome recorded was work completed. A separate quote was issued for the open air bender in the duct system; that work is pending a decision from the homeowner.
If you have a Hitachi ducted or split system that needs attention, our team services and repairs the full Hitachi range across metropolitan Adelaide. For any ducted fault or repair, see our air conditioner repairs page. If you are weighing up the cost of a repair against a new system, the repair or replace calculator can help.
“A run capacitor is a small part with a continuous job. Catching a failed one during a service, before it has had the chance to damage the fan motor, is almost always the better outcome.” Oliver Hastings, T&K Airpower
Frequently Asked Questions
Why is my ducted air conditioner running but not cooling?
Several faults can produce this, including a failed run capacitor on the condenser fan motor, a refrigerant leak, a blocked condenser coil, or a compressor fault. A run capacitor failure is one of the more common causes and is a straightforward repair. If the outdoor unit is running but cooling is poor, a service call is the right first step.
What does a run capacitor do in an air conditioner?
A run capacitor provides a continuous electrical phase shift to the fan motor’s auxiliary winding, which keeps a single-phase motor turning smoothly under load. Without it, the motor may hum without starting, run slowly, or draw excessive current and generate internal heat.
How do I know if my AC capacitor has failed?
Common signs include an outdoor unit that hums but does not start, a fan blade that spins slowly or not at all, and a system that runs for long periods without reaching the set temperature. A technician can check the capacitor’s microfarad value to confirm whether it has fallen below the motor’s rating.
Is it safe to run an air conditioner with a failed run capacitor?
Continuing to run a system with a failed or marginal run capacitor puts the fan motor at risk. The motor is forced to draw more current than it is rated for, which generates heat and shortens its working life. The sooner the capacitor is replaced, the lower the risk of a secondary motor failure.
How much does it cost to replace a run capacitor on a ducted system in Adelaide?
As a guide, a condenser fan run capacitor replacement on a ducted system is $500 to $600 inc GST (correct at 4 November 2026). A ducted service on its own is $290 inc GST. Prices vary by system, age, and access. Call T&K Airpower on 08 8296 7888 for a quote specific to your system.
Can I replace a run capacitor myself?
No. Capacitor replacement on an air conditioning system is electrical work that must be carried out by a licensed technician. Run capacitors also retain a stored charge after the power is disconnected and require safe discharge before they can be handled. Attempting this without the correct training and equipment is not safe.
How often should a ducted air conditioner be serviced in Adelaide?
An annual service before summer is the standard recommendation for most ducted systems. A service checks filters, airflow, electrical components, and the condition of parts like run capacitors, all of which can go undetected without opening the outdoor unit. See our service and maintenance page for details and pricing.
Need Help?
If your ducted air conditioner is not cooling or is due for a service, call T&K Airpower on 08 8296 7888 or book online via our contact page. We have been servicing and repairing air conditioning systems across Adelaide since 1996. We are licensed, insured, and authorised warranty agents for Mitsubishi Electric, Hitachi, and Temperzone. Our approach is repair first, and we will give you an honest assessment of whether a repair or a replacement is the better value for your situation.
