What was found
APU WILL NOT START, FAULT LIGHT ILLUMINATED. GROUNDED - YES. APU BITE TEST SHOWS MSG 49-15004, INLET DOOR SHUT DOWN IAW B737-800 FIM 49-10 TASK 806, REMOVED AND REPLACED AIR INLET DOOR ACTUATOR IAW B737-800 AMM 49-15-31. ACCOMPLISHED AIR INLET DOOR TEST REF AMM 49-15-00-700-801 WITH NO DEFECTS NOTED. THIS IS AN INTERMITTENT FAULT WITH A LONG HISTORY. OTHER POSSIBLE CAUSES LEFT ARE APU FUEL SHUT OFF VALVE ( P/N AV16E1209D) AND A WIRING PROBLEM. APU START OPS CHECK NORMAL 4 TIMES.