What was found
LT - FLT 3667 - AFTER ADJUSTING TEMPERATURE ON RT TEMP SELECT, DUCT TEMP WENT TO 100 DEGREES CELSIUS. OVERHEAT CAUTION CAME ON AND F/A REPORTED SMOKE IN THE CABIN COMING FROM AIR DUCTS. PERFORMED QRH PROCEDURES. TURNED OFF NR 2 PACK AND SMOKE STARTED TO CLEAR. SMOKE DID CLEAR COMPLETELY WITH NR 2 PACK OFF. CONTINUED TO DESTINATION LIT. THERE WERE NO RECIRC FAN FAULTS. SUBMITTER SUSPECTED NR 2 PACK/ACM FAILURE. MEL 21-23. REMOVED AND REPLACED AIR TRIM VALVE. OPS CHECK GOOD. MEL 21-23 RESTORED. (X)