What was found
APU WILL NOT CRANK. GROUNDED - YES. REMOVED AND REPLACED BOTH AIRCRAFT BATTERIES REF AMM 24-31-11. APU STILL WILL NOT START ON JUST BATTERY POWER. APU STARTS ONLY ON GROUND POWER. AFTER FAILED BATTERY START APU BITE SHOWS MSG 49-15004 (INLET DOOR SHUTDOWN). VERIFIED APU INLET DOOR OPEN ON AC STARTS. FOUND INLET DOOR POSITION SWITCH RIGGED INCORRECTLY. ADJUSTED SWITCH, REF AMM 49-15-11. ACCOMPLISHED TWO SUCCESSFUL APU BATTERY STARTS, REF AMM 49-11-00.