I will be having a new Trane 2.5 or 3 ton XR12 split ac system installed soon. I feel pretty good about the contractor that will be performing the install, but would like some general recommendations from you guys. I want to know if it is imperative that the installer flow nitrogen when soldering or brazing the lines, or is this just an extra measure that is not really necessary. Also, which is the better or preferred method , soldering or brazing? Approx. how long should a new system be evacuated after the install? Should I request that an inline filter/dryer be installed at the time of installation?