What was found
ON FLIGHT DECK PREFLIGHT, EICAS MSG L PACK TEMP FOLLOWED BY L PACK OFF 2 MINS AFTER SELECTING LEFT PACK OFF(<P>TRANSFERRED TO MDDR 151815 PER DDG 21-51-03-01, CAT C. REACTIVATED LT PACK IAW AMM 21-00-00, REMOVED AND REPLACED LT PACK LOW LIMIT VALVE IAW AMM 21-51-11. OPS CHECKED GOOD, LEAK CHECKED GOOD. PERFORMED FIM 21-51-844, SYSTEM IS SATISFACTORY. OPS CHECKED PACK FOR 2 HOURS, NO DEFECTS NOTED.