What was found
AFTER TAKEOFF, THE PILOT NOTICED SMOKE IN THE CABIN AFTER THE AIR CONDITIONING VALVE STARTED OPENING TO PRESSURIZE THE ACFT. ACFT RETURNED TO BASE. TROUBLESHOT AIR CONDITIONING SYS, COULD NOT DUPLICATE. INSPECTED ENGINE OIL LEVELS FOR OVER SERVICING, NO DEFECTS NOTED. INSPECTED COOLING TURBINE, NO DFECTS NOTED. RAN ACFT AND GROUND CHECKED PRESSURIZATION SYS, NO DEFECTS NOTED. SUSPECT ACFT DE-ICING FLUID WAS INDUCED INTO 1 OF THE ENGINES WHILE PARKED ON RAMP. ACFT TEST FLOWN WITH NO ISSUES.