What was found
SEA - AIR TURN BACK OF FLT 442 - CREW REPORTED HYDRAULIC FLUID ODOR IN CABIN. REPLACED BOTH WATER SEPARATOR COALESCERS, NO CONTAMINATION OR ODOR NOTED. ODOR APPEARS TO BE COMING FROM RIGHT AIR CONDITIONING PACK. REPLACED RIGHT COOLING TURBINE, ODOR STILL PRESENT. RELEASED WITH RIGHT AIR CONDITIONING SYSTEM INOPERATIVE PER MEL 21.1. OPERATED AIR CONDITIONING PACKS WITH ENGINES AND APU AS AIR SOURCE. FOUND ODOR TO BE COMING FROM APU. REPLACED APU AND OPERATED PACKS WITH APU AS AIR SOURCE, NO ODOR OR DEFECT NOTED. (M)