no, but my ex GF had a 200sx and all of the refrigerant leaked out so I charged it myself since it's a 134a system, worked like a dream
I'd look for 15-20 degrees, though that isn't the best way to determine it's operation IMO but if I got 15 I'd be happy
Not sure what you mean by split (difference?) but on an average hot day, I always liked to see temps below 55 (at idle and cruise). Ive seen them at 32 and up to the low 60s that were still cooling comfortably. It all depends on the efficiency of your car(i.e. tinted windows, no sunroof, etc). When checking at the vents, use an a/c thermometer, turn the a/c to max, recirculate on (if applicable) and turn the fan to about mid way. If you turn the fan all the way up, you will get a higher reading. Some systems can vary 10-15 degs between sitting at idle and at cruise speed.
bill- he's talking about the temp difference between the hot air going into the cooling coil compared to the cold air coming out.
I've only used it to check home systems where we look for about 20 usually, but that's tested right above and below the cooling coil which is why I'd be happy with 15 in a car, maybe that's too low. Beats me.