What was found
MUSTY SOCK SMELL FROM PACKS W APU BLEED RUNNING OILY MUSTY SMELL WITH PACKS RUNNING ON APU. PLACED APU ON MEL MEL 4910B REJECTED NEED TO ADDRESS THE ODOR IN THE CABIN ACP INITIAL TROUBLE SHOOTING PER FIM TASK 05-50-00-810-831-A , CONFIRMED ORDER STRONG WHEN APU AND RUNS RUNNING. ISOLATED PACKS SMELL STRONG WHEN EITHER PACK RUNNING. CW DEFERRAL PULLED BREAKERS L 41 AND 42. ACFT PACK OPS, NO SMELL NOTED IN ANY COMBINATION OF SOURCES OR PACK SETTINGS. APU REPLACEMENT WILL BE REQUIRED TO CORRECT THE SOCK SMELL IN CABIN/ FLIGHT DECK REMOVED APU IAW AMM 49-11-11. REQUIRES INSPECTION OF APU FIREWALL. C/W APU FIREWALL INSPECTION PER AMM 49-11-11. NO DEFECTS NOTED. OK TO INSTALL NEW APU ASSY. REF TO JOB CARD #20-4900-1-0005 FOR R/R OF APU, AND RII INSPECTION. OPS CHECK GOOD, NO LEAKS. NO MUSTY SOCK SMELL WHEN RUNNING APU BLEED WITH PACKS ON.