My HVAC contractor installed two linesets, one from my basement apartment, one from the main unit, both going to the roof where the air condensers are. The problem is, he did it over several days and I have a suspicion that he messed up which pipe/wire goes where, i.e. that he mixed them. He claims that he marked it along the way but I am skeptical. Both linesets (fat and skinny flex copper, power supply, and thermostat) enter the roof through lead cones. It is not possible to trace the pipes along the way because most of their way is now blocked to sight. Only the linesets have been installed thus far, so there is no air handler/condensers installed on their end, so the pipes are empty.
Is it possible to use a small amount of current (from a battery?) and send it on one end of the pipe while checking it with a multimeter or some voltage detector on the other end? If yes, how should I rig up such a contraption? Can I just wire the battery onto the pipe?