Why 20psi, not 15??

[smorgan87]

Once upon a time i was working on a residential ac system that kept leaking down. I never could find the leak with a sniffer because it was small and was in the condenser so the fan kept any gas from being detected. I filled her with nitrogen and about 50 psi from the systems max test psi i found it when the small pinhole became a not so small hole. Sometime parts need to be pushed to their max for diagnostics. In a trucks case like rawze said its better to fail it in ur garage/driveway than on the shoulder of i20 100 miles from nowhere.