Arrived on 28 December for a fall tuneup check capacitors on the inside and outside of the unit everything‘s within tolerance it was warm enough outside to check the charge on the unit it had 23° superheat with 25° sub cooling it is an R 22 system with TXV is on the inside and outside unit Heat exchanger checked flame sensor hot surface igniterGas pressure everything’s within tolerance this is an old unit and I would recommend replacing it at the earliest convenience customer changes on filters. Recommended due to his age that the homeowners acquire more carbon monoxide detectors in the home did not find any while testing unit but still recommend carbon monoxide detectors.