As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER STARTING THE APU AND OPENING THE BLEED AIR SUPPLY SWITCH, THE CABIN FILLED WITH MIST AND HAZE. THE DUCT TEMPERATURE WAS HIGH. MAINTENANCE TROUBLESHOT IAW WORK CARD 2120-2367 AND FOUND A HYDRAULIC LEAK AT THE LEFT REVERSER CONTROL VALVE. A B-NUT WAS SECURED AND LEAK CHECKED GOOD. AN ALTERNATE DUCT BURNOUT WAS PERFORMED PER WORK CARD 4950-2215. THE COALESCER BAGS WERE REPLACED. (LP9692817)