What was found
AFTER STARTING THE APU, WE WAITED APPROXIMATELY 3 MIN BEFORE THE BLEED AIR WAS TURNED ON. WITHIN 15 SECONDS OF TURNING THE APU BLEED AIR ON, THE CABIN STARTED TO FILL WITH A DUSTY HAZE. WE SHUT THE BLEED AIR OFF AND THE HAZE SLOWLY SUBSIDED. APPROX 1 MIN AFTER THE BLEED AIR WAS SHUT OFF, WE SHUT THE APU DOWN WITH NO ISSUES. THE HAZE THAT FILLED THE CABIN WAS AS A DUSTY TYPE HAZE THAT HAD A HOT DUSTY SMELL TO IT. PERFORMED APU TROUBLESHOOTING PER M/M 49-00-00 AND M/M 49-25-85. INSPECTED AND CLEANED APU INLET AND EXHAUST. PERFORMED DUCT BURN OUT TASK CARD TC-5XL21-120902M. REPLACED WATER COALESCER. PERFORMED APU INLET CLEANING AND POST RUN CHECKS. NO DEFECTS NOTED AT THIS TIME.