As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
CREW REPORTED A BURNING SMELL JUST AFTER BLEEDS WERE SWITCHED FROM APU TO ENGINES AFTER TAKEOFF FROM CLT EN ROUTE TO OAJ. THE LEFT AIR CONDITIONING PACK WAS FOUND TO BE CAUSING THE SMELL. MAINTENANCE TROUBLESHOT THE AIRCRAFT, REMOVED AND REPLACED THE LEFT PRESSURE REGULATING SHUTOFF VALVE (PRSOV) FILTER AND PERFORMED CHECKS USING THE AIRCRAFT MAINTENANCE MANUAL. AIRCRAFT WAS RELEASED FOR SERVICE.