What was found
WHEN APU STARTED & BLEED AIR VALVES OPENED, SMOKE BEGAN TO POUR OUT OF VENTS. SMOKE DISSIPATED WHEN APU BLEEDS CLOSED. WHEN ENG STARTED, NO SMOKE WAS OBSERVED. R & R COALESCER SOCK & COMPLIED WITH ENVIRONMENTAL CONTROL SYS, ECS, DUCT BURN OUT FORM IAW TC-680-21-120905M. OPERATIONAL CHECKED GOOD. NO LEAKS NOTED.