Unless you mean 30Psi this makes no sense. You would also want to go colder as close to 32F as possible. You can apply head pressure and let it set for a few days or do the old shake the keg to do it in minutes. Either way you wont be extremely consistent though you can get pretty close. Go to the Meheen or Zham site and download the carbonation chart for reference. You will need between 10-15Psi to maintain carb depending on levels and temps so 3psi is pointless.