From Brian Vick (via e-mail)

I would like to know the proper way to charge a home central a/c unit. Rule of thumb was always to take the ambient at the condensing unit and add 30°F, then convert it to psig. Is this still the norm? I did this on a Janitrol 3.5-ton and a 3.5-ton Sears unit, and they both are running well.