What was found
MNL - FLT 879 - ON GROUND IN MNL, CREW STARTED APU. AFTER APPROXIMATELY 8 MINUTES RECEIVED APU FIRE WARNING. CREW C/W EMERGENCY PROCEDURES TO PULL FIRE HANDLE AND FIRE BOTTLE. PER CREW COMMENTS, APU GENERATOR OPERATED NORMALLY - 116 VAC 403 CYC. FREQUENCY AND EGT ALSO REPORTED NORMAL. REMOVED APU SHROUD PANELS AND CHECKED FOR EVIDENCE OF FIRE. NO EVIDENCE OF FIRE FOUND DURING INSPECTION. RE-INSTALLED AND SECURED PANELS, DEACTIVATED APU PER DDP 49-1 AND SECURED INOPERATIVE APU PER MM 49-00, PAGE 220. AIRCRAFT RELEASED PER MEL 49-01. SUSPECT APU FIRE OVERHEAT AND DETECTOR UNIT AS THE SOURCE OF FALSE WARNING. FOUND MOISTURE AROUND UNIT AFTER VERY HEAVY RAINFALL. (X)