What was found
WHEN SWITCHING FROM APU BLEED AIR TO MAIN AIR VALVES, AFTER TAKEOFF NOTED STRONG ACRID ODOR COMING FROM AIR CONDITIONING DUCTS. WHEN TAXING IN, ODOR WOULD INCREASE WHEN CHANGING BLEED AIR SOURCE. PERFORMED APU AND ENGINE RUN WHILE SWITCHING BLEED AIR SOURCE AT TAKEOFF POWER. NO ODOR NOTICED. CHECKED THE WATER SEPARATOR APU DUCTING, APU ENCLOSURE, MAIN AIR VALVE DUCTING. NO DEFECTS NOTED. PERFORMED ANOTHER ENGINE RUN, CYCLING TEMP CONTROL FROM FULL COLD TO FULL HOT WITH BOTH APU AND ENGINE BLEED AIR. NO ODOR NOTED. FOUND THE RT ENGINE OIL TO BE OVERSERVICED. DRAINED TO CORRECT LEVEL IAW AMM 71-00-00, 21-10-00. 21-10-95.