What was found
ON DESCENT 5000, POWER IDLE-CONTROL CABIN SUPPLY DUCT TEMP INCREASED TO 43 DEG. CONTROL CABIN TEMP SELECTOR MOVED TO FULL COLD: AND TEMP REMAINED AT 43 DEG C. ACFT GROUNDED. FOUND PACK TEMP CONTROL VALVE TRYING TO DRIVE BEYOND CLOSED WHILE PACKS WERE NOT RUNNING AND ALL SWITCHES IN THE OFF POSITION. SUSPECT VALVE CANT FIND ITS NULL POINT, VALVE WAS HOT TO THE TOUCH AS THE VALVE WOULD NOT STOP TRYING TO DRIVE CLOSED. HUNG NEW VALVE AND PROBLEM WENT AWAY. REQUIRES NEW LT PACK TEMP CONTROL VALVE. REPLACED TCV REF MM 21-51-10-400-801. OPS CK NORMAL.