Why is my two year old A/C compressor cycling every 10 seconds?
The technicians found low refrigerant and a slow leak at the fill valve.  They replaced the valve, refilled and tested the system and all seems well.
This leaves annoying open questions that can no longer be answered including:

Why did the self-diagnostic
detect Locked Rotor (4) and not Low Charge (1)?
How did a &quot;slow leak&quot; spontaneously develop after the end of last summer that progressed as far as immediate low-pressure-shutdown for the beginning of this summer?

The technicians were not interested in contemplating these things so I'll just have to move on without answers but with a working system.