What was found
RAN APU WITHOUT BLEED FOR 8 MINUTES BEFORE TURNING ON BLEED WHEN BLEED TURNED ON DIRTY SOCKS SMELL STARTED, RAN WITH BLEED FOR ABOUT 1 MINUTE AND THE SMELL GOT STRONGER, TURNED BLEED OFF SMELL WENT AWAY. FLIGHT ATTENDANTS DID NOT SMELL IT BUT BOARDING DOOR WAS OPEN. APU SYSTEM MEL NUMBER ADDED FOR DISPATCH RELEASE, LOG REDEFERRAL REQUIRED. C/A: DEFER APU PER MEL 49-10-01A. SUSPECT APU INLET CONTAM PER STEP I. MEL AND PLAC INSTALLED, "M" PROC C/W. (LP: 8256600)