What was found
FOR FLIGHT 3771 THE CREW REPORTED THAT WITH LEFT ENGINE RUNNING AND LEFT PACK ON, JUST AFTER RIGHT ENGINE START GOT AIR CONDITIONING SMOKE IN THE CABIN. THE CREW SHUT DOWN RIGHT THE ENGINE AND THE LEFT PACK. THE SMOKE IMMEDIATLY BEGAN TO CLEAR. THE CREW ALSO RECEIVED A LEFT PACK AUTO FAIL EICAS MESSAGE JUST AFTER THE RIGHT ENGINE WAS SHUT DOWN. THE AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED THE NR 2 AIR CYCLE MACHINE IAW CRJ-700 AMM 21-51-08. THE OPERATIONAL CHECK WAS GOOD. THE AIRCRAFT WAS RETURNED TO SERVICE.