What was found
SLIGHT BURNING ODOR IN THE ACFT AT FL 210. OUTSIDE RAM AIR TEMP WAS 12 DEGREES C. NO SMOKE WAS PRESENT. NO UNUSUAL ODOR OR BURNING SMELL WAS NOTICED. STARTED APU FOR POWER AND BLEED SOURCE, OPERATED ALL CABIN SYSTEMS WITH NO ABNORMAL SMELLS. VISUALLY INSPECTED THE COFFEE MAKER, ALL CABIN ELECTICAL OUTLETS, AND CABIN CONTROL DEVICES WITH NO OVERHEAT EVIDENCE. STARTED BOTH ENGINES FOR T/S, ISOLATED BLEED SOURCE FROM EACH ENGINE AND APU SUPPLY AND DID NOT IDENTIFY ANY ABNORMAL OR BURNING SMELL. REF AMM 21-20-00 AND 36-10-00. ALSO PERFORMED BLEED AND TRIM AIR DUCT BURN PROCEDURE WHICH INCLUDES REPLACING THE HEPA FILTER REF ITEM 2.4 OF THIS WORKORDER NO BURNING ODORS APPEARED.