What was found
WHILE IN CRUISE FLIGHT AT FL340, AUTOMATIC TEMPERATURE CONTROL WAS LOST AND THE CABIN STARTED CLIMBING AT 700-800 FPM. AN EMERGENCY DESCENT WAS INITIATED WHEN THE CABIN REACHED 10,000 FT. CABIN ALTITUDE MAXED OUT AT 11,500 FT AND THEN BEGAN TO DESCEND. FLIGHT CONTINUED TO DESTINATION AT 10,000 FT MSL AND LANDED WITHOUT ANY OTHER COMPLICATIONS. MAINTENANCE AT DTW FOUND A DUCT CRACKED & OPENED AND REPLACED IT. ALSO REPLACED TEMPERATURE CONTROLLER. LEAK CHECK WAS GOOD AND THE AIRCRAFT HAS RETURNED TO SERVICE.