Outdoor Unit Buzzing and Clicking: Capacitor, Not Compressor

Something outdoors that hums briefly when it should start, then falls silent, with the fan behaving perfectly normally. Cooling has stopped completely. The compressor is being quoted as the cause of it.

A hum with no rotation is a specific symptom and it is not proof of a failed compressor. It describes a motor receiving power and not being given enough help to overcome the load and begin turning. The component whose entire job is to provide that help is inexpensive, accessible and much shorter-lived than the compressor it serves. Testing it takes minutes, and it has to be eliminated before anything larger is put on a quote.

A compressor needs considerably more effort to begin turning than it does to keep turning, and a small component stores and releases the energy that provides it. That component degrades with heat and age, losing capacity gradually. Once it falls far enough, the compressor is given power and not enough assistance, so it draws current, hums and does not move at all. The compressor itself is untouched by any of this.

The starting component is replaced and the unit runs normally again, at a small fraction of what was being discussed. The order of investigation is the whole lesson here. Anything that fails to start should have its cheap starting components eliminated first, because they are the shortest-lived items in the circuit and the symptom they produce is indistinguishable from the expensive alternative.