Does any one know the correct procedure for recharging an AC unit with the newer type refrigerants? I've heard that you need to replace all hoses, o-rings and accumulater/dryer unit before recharging and others say that you only have to change the o-rings and accumulater/dryer unit? I would prefer to do all the mechanical work myself and then bring it to a good shop for charging. Can anyone recomend a good ac shop in the Boston,MA area?