Here's what I do when I need to force carb in a hurry:
- Connect keg to C02 tank, purge air from keg by pulling the pressure release valve a couple of times
- Set keg pressure to 30-PSI and leave overnight in keezer to chill
- In the morning, keg is now chilled, remove keg from keezer and shake back and forth while counting to 100. You will hear C02 entering the keg as you do this
- After shaking keg, drop C02 pressure to normal serving pressure (normally 10-12 PSI)
- Purge excess C02 from keg by pulling pressure release valve on keg once or twice
- Carefully pour a beer through the tap (the first one may come out a bit forcefully)
After doing the above I have a decent amount of carbonation and head on my beer after a total of about 14-hours.