Yeah but if he's in a position to visually verify that the coil is in fact freezing over he can report that as a symptom and maybe save defrosting on the clock. It's not like he'd be telling the guy what is wrong or how to fix it, only that air flow slows and stops after it runs x hours and he looked at the coil and it was an ice cube. That extra hour of tech time might be better used watching it *start* to freeze over.