As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR DUCT OVER HEAT CABIN (ENVIRONMENTAL DUCT OVERTEMP) REACHED A TEMP OF 325C AND WAS INCREASING AND SMOKE IN THE CABIN IN-FLIGHT. FOLLOWED CHECKLIST Q4 AND TEMP DECREASED TO 208C. TROUBLESHOT "AIR DUCT O' HEAT CABIN" LIGHT, CABIN SUPPLY AIR UNCONTROLLABLE IN MANUAL MODE, FOUND TEMP CONTROL VALVE FOILED, R & R CABIN TEMP CONTROL VALVE WITH AN O/H UNIT IAW MM CH 21-31-00. OPS CHECKED GOOD.