Purchased a new Goodman 3 ton heat pump . (split system ) I have everything installed except the copper line set. The set is 3/4 - 3/8 . This system has an alum evaporator and a copper line welded in for the set. It is welded closed. When I cut the end off it is much bigger than the 3/4 line that I wish to braze into. What is used for this ?