What was found
DURING CRUISE, WITH THE LT PACK DEFERRED, AT APPROXIMATELY 25,000 FT THE CREW RECEIVED A MASTER CAUTION (CABIN ALT) MESSAGE. WHILE COMPLYING WITH THE QRH, A MASTER WARNING (CABIN ALT) MESSAGE WAS RECEIVED. THE CREW PERFORMED AN EMERGENCY DESCENT AND DECLARED AN EMERGENCY. THE AIRCRAFT LANDED SAFELY. MAINT DETERMINED THE ABOVE EVENT OCCURRED DUE TO PACK OVERPRESSURE AND IT AUTO SHUTDOWN. MAINT GROUND RAN THE RT ENGINE WITH DUCT PRESSURE AND PACK PRESSURE BEING NORMAL. OPS CHECK GOOD. AC OK FOR SERVICE. (K)