What was found
ACRID ODOR IN THE COCKPIT, IN BEGINNING DESCENT. NO SMOKE OR OBSCURATION. INTENSE ODOR FOR 15-20 SECONDS THEN RAPIDLY DISSIPATED . NO ENGINE OR WING ANTI-ICE. NOT LIKE AN ELECTRICAL BURNING ODOR. ODOR OCCURRED THREE TIMES DURING DESCENT ON PREVIOUS FLT . ON THIS FLIGHT, ODOR OCCURRED ONCE DURING TAKEOFF (NOT A STRONG) AND ONCE DURING DESCENT(INTENSE). ODOR DOES NOT COME FROM ANY PARTICULAR AREA OF COCKPIT. REMOVED AND REPLACED LT & RT OZONE CONVERTERS. LEAK CHECKED GOOD. RAN PACKS ON APU AIR WITH NO ABNORMAL ODORS NOTED. RAN ENGINES NR 1 & 2 WITH PACKS ON, NO ABNORMAL ODORS NOTED IAW AMM 21-51-22-4.