What was found
VISIBLE SMOKE & SMELL OF BURNING RUBBER IN CABIN ON GND. VISUALLY CHECKED OIL LEVEL OF APU WITH NO DEFECTS NOTED. CHECKED COALESCER SOCKS OIL. OPERATED APU, BOTH COCKPIT & CABIN PACS, NO SMOKE SMELL NOTED. HEAVY CONDENSATION SMOKE FROM ALL EYELETS. OPERATED BOTH PACS TO 42 DEGREES COLD TO HOT. OPERATED AVIONICS & CHECKED FOR ANY BURNT SMELL IN THE AFT CLOSET AREA OF THE ACFT WITH NONE NOTED. BORESCOPED APU INLET FAN WITH NO DEFECTS NOTED. PERFORMED LT & RT ENG GND RUNS FOR APPROX 45 MIN EACH, NO OIL SMELL OR SMOKE. OPERATED APU A TOTAL OF 5 HOURS. OPERATED APU ONE HOUR WITH PACS & ALL SYS ON WITH NO SMOKE OR BURNING SMELL NOTED IAW AMM 49-00-00 21-51-00 & 21-00-00. OPERATIONAL CHECKED SATISFACTORY.