What was found
DURING THE CLIMB OUT, WHEN PASSING THROUGH 2,000 FEET THE CREW EXPERIENCED THE OPENING OF THE EMERGENCY PRESSURIZATION VALVE CAUSING THE CABIN TEMP TO INCREASE AND LIGHT SMOKE/"HOT" SMELL IN THE CABIN. AT THIS TIME THE CREW DECLARED AN EMERGENCY, MANUALLY DROPPED THE PAX OXYGEN MASK AND RETURNED TO THE DEPARTURE AIRPORT WITHOUT INCIDENT. DURING THE EVALUATION BY MAINTENANCE PERSONAL IT WAS DISCOVERED THAT THE INLET SIDE OF THE AIR CYCLE MACHINE HAD SUSTAINED DAMAGE FROM WHAT APPEARS TO BE INLET TURBINE FAILURE.