What you'll notice
The outdoor unit hums or buzzes audibly but the compressor never spins up. After a few seconds the internal overload cuts it out, and the cycle may repeat.
Why it happens
Almost always a failed start or run capacitor, or a compressor whose windings or mechanical bearings have seized. The hum is the motor energised and straining against a load it cannot turn.
A humming outdoor unit that will not start is one of the more diagnosable aircon faults, because the sound itself narrows the possibilities considerably. The motor is receiving power — that is what you are hearing — but it is not turning.
Capacitor first, always
Capacitors are consumable. They degrade with heat cycling, and South African summers are hard on them. A capacitor rated at 35 microfarads that now measures 12 will produce exactly this symptom. Testing takes minutes and the part is inexpensive, which is why any competent diagnosis starts here rather than with assumptions about the compressor.
If the capacitor is good
A seized compressor produces the same hum, and at that point the conversation turns to the age and value of the unit. On an older system the sensible route is often replacement rather than repair, and we would rather have that conversation honestly up front than after you have paid for a diagnosis that leads nowhere.
How we fix it
We test the capacitor against its rated microfarad value, which is a quick and definitive check, and only if that passes do we insulation-test the compressor. Where a capacitor is at fault the repair is usually completed on the same visit.
Still not working?
If the checks above haven't restored your compressor, this usually needs a technician. Our Aircon Repairs service covers exactly this fault — from R650, quoted upfront.