What was found
ON FLIGHT 4371 THE CREW REPORTED THAT DURING TEST OF RECIRC FAN PER MEL 21-29, THEY HEARD A LOUD GRINDING NOISE AND EXPERIENCED SMELL OF HEAVY SMOKE/ FUMES. THIS OCCURED WITH APU BLEED OPEN, X BLEED OPEN AND BOTH PACKS SELECTED OFF. OPERATED APU, NR 2 PACK AND RECIRC FAN. NO GRINDING SOUNDS OR ODOR FOUND. SUSPECT POSSIBLE INADVERTANT USE OF DEFERRED NR 1 PACK REF EMB 140 AMM 21-60-00. REMOVED AND REPLACED NR 2 PACK VALVE AND THE OPERATIONAL CHECK WAS GOOD IAW EMB AMM 21-51-01. MEL RESTORED. THE AIRCRAFT WAS RETURNED TO SERVICE.