What was found
AIRCRAFT WAS GROUNDED. AFTER TAKEOFF DURING CLIMB CABIN PRESSURE AND TEMPERATURE WERE UNCONTROLLABLE CABIN ALT CLIMBED TO 9400' AND WAS STILL CLIMBING FLIGHT DECK TEMP CLIMBED TO 96 DEG AND THE CABIN WAS 89 DEG WITH NEGLIGIBLE AIRFLOW. AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO DFW, WHERE IT LANDED SAFELY WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND THE RIGHT HAND PACK LOWER RECIRCULATION FAN CHECK VALVE BROKEN AND DUCT BOOT SLID OFF OF DUCT. REPLACED RECIRCUALTION FAN AND ACCOMPLISHED A SATISFACTORY LEAK AND OPERATIONAL CHECK, PER AMM 21-25-17.