As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
APU ON & BLEED ON, TEMP WENT RAPIDLY TO 250 DEGREES & THEN AIR DUCT O'HEAT ANNUNCIATOR ILLUMINATED, FOLLOWED BY A VERY STRONG ACRID SMOKY SMELL IN THE CABIN. BLEED AIR WAS TURNED OFF & FULL MANUAL COLD SELECTED, BUT THE SMELL OF SOMETHING BURNING CONTINUED. APU WAS SECURED. NEED EVALUATION FOR COLLATERAL DAMAGE. R & R THE TEMP CONTROL DISPLAY UNIT IAW MM 21-51-00. SYS OPERATIONS CHECKED GOOD.