What was found
CREW REPORTED TRACES OF SMOKE FROM THE LOWER LT SIDE OF THE COCKPIT ON DESCENT. DONNED OXYGEN MASKS FOR LANDING. TURNED HI-FLOW OFF AND LT BLEED , SMOKE SEEMED TO DISAPATE. MX PERFORMED ENGINE RUNS FOR 30 MINS WITH NO SIGNS OF SMOKE OR VAPOR. CHECKED UNDER LT INSTRUMENT AND BEHIND CB PANELS AND FOUND NO SIGNS OF ARCING AND NO ELECTRICAL ODOR NOTED. CHECKED FOOT WARMERS FOR SIGNS OF OVERHEAT. NO DEFECTS NOTED. MX DID NOT HAVE ACCESS TO BOROSCOPE TO CHECK APU. APU DEFERRED PER THE MEL AS A PRECAUTION UNTIL BOROSCOPE IS AVAILABLE.