What was found
AIR RETURN, STRONG BURNING SMELL STARTED IN REAR OF ACT DURING CLIMBOUT APPOX 1000FT MCT POWER SETTING. ODOR QUICKLY CONTINUING TO MOVE FORWARD TO FRONT CABIN THEN FLIGHT DECK. CLEANED OIL CONTAMINATION IN LT A/C BAY, REMOVED AND REPLACED PRIMARY MAIN HEAT EXCHANGER, REHEATER, REMOVED, CLEANED, & REINSTALLED ACM, CONDENSER, & WATER EXTRACTOR. REMOVED AND REPLACED RECIRCULATION FILTER CARTRIDGES. ALL WERE REPLACED FOR PREVENTATIVE MAINTENANCE.