Best rule of thumb I have seen is to charge to a high-side pressure (in psi) of 2.2 to 2.5 times the air temp (in F) in front of the condenser/grille. That's how I do all my cars.
If you're charging to 250 psi on an 80F day I think that's too much.


Oh, and drain and flush as much of the old mineral oil as you can. It doesn't mix with the PAG oil used for R-134a, so it's taking up space in the system somewhere (even if it just sits in a low spot, usually the receiver/dryer).