Should the air conditioner line set be replaced when a new air condition is put in?

The question is, why is a new air conditioner being put in? If the old air conditioner was only a few years old but was simply too small, the answer is probably not unless the old line is inadequate for the power. If the old air conditioner was a number of years old and wore out, then there is the question of the quality of the line. Wiring wears out. Insulation wears out. If the wiring or insulation shows any sign of wearing out, then by all means, replace it. It is far less expensive to replace it when you are putting in the new unit than to have an electrician come in and replace it at a later date. If it has aluminum wiring, replace it yesterday.