Help, please. The 15 year old 10 SEER split AC/NG furnace is ripped out (Ugh! - at least 95 today and tomorrow). The rebuild of the plenum for larger coil and new MERV 11 filter planned. The new York 18 SEER YZH04811C HP and 80% VS YP8C100C20MP11A NG furnace are ready to go. Aspen coil , TXV and mandatory (rebate) UV lights are ready too.
Really concerned with the cleaning of the reused line set which the contractor proposed. It's buried in the garage floor and snaked through a vent soffit to behind the furnace. The tech seems intent on just putting a vacuum pump on it to clean it and then load up the R410a. What I have heard here at a minimum is a nitrogen flush is required to rid the line set of the R22 mineral oil. Others add an RX11 flush. Please advise ASAP what is required.