What was found
DURING DECENT AT FLIGHT IDLE, A BURNING ODOR OCCURED. DUCT TEMPERATURE WAS AT 0 DEGREES, SWITCHED THE TEMP CONTROL TO MANUAL AND INCREASED INPUT TO WARM. ODOR DISSAPTED. DURING ENGINE RUNS BLEEDS OFF, NO ODORS NOTED, WITH NR 2 BLEED ON FULL COLD NOTICE OIL ODOR. TURNED NR 2 BLEED OFF, ODOR DISIPATED. TURNED NR 1 BLEED ON ODOR RETURNED. TURNED NR 1 BLEED OFF, ODOR DISIPATED. SUSPECT FAULTY AIR CYCLE MACHINE. REMOVED AIR CYCLE MACHINE. INSTALLED REPLACEMENT AIR CYCLE MACHINE IAW AMM 21-50-11. SERVICED REPLACEMENT AIR CYCLE MACHINE, IAW AMM 21-50-11. FOUND WARPED HEAT EXCHANGER HEADER DUCT R & R DUCT OPS AND LEAK CHECKS GOOD IAW MM 21-50-16.