What was found
WHILE STARTING APU, CABIN IMMEDIATELY FILLED UP WITH THICK, ACRID SMOKE. REMOVED APU IAW MM 49-10-00. DRAINED REMOVED APU OF OIL. CLEANED APU CONTAINMENT BOX & FLUSHED DRAIN LINES. INSTALLED APU IAW MM 49-10-00. R&R CONDENSER SOCK, PN 83237-12, IAW MM 21-51-00. SERVICED APU OIL IAW MM 12-11-02. OPS CHECK & LEAK CHECK SATISFACTORY ON APU RUN. IAW MX CONTROL, COMPLETED ECS DUCT BURN OUT. R&R WATER SEPARATOR CONDENSER SOCK, POST ECS BURN OUT PROCEDURE IAW MM 21-51-00. PRESSURIZED ACFT TO 8 PSI FOR LEAK CHECKING WATER SEPARATOR ASSEMBLY. LEAK CHECK SATISFACTORY OF WATER SEPARATOR ASSEMBLY ON PRESSURIZATION RUN. INSTALLED APU ENCLOSURE BOTTOM ACCESS PANEL & APU OUTER COVER PANEL REMOVED FOR ACCESS.