A B737-300 DEPRESSURIZED FOLLOWING A PACK FAILURE WITH 1 PACK PREVIOUSLY ON THE MEL BY MAINT.

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L PACK DEFERRED. R PACK RAM AIR DOOR DEFERRED OPEN PREVIOUSLY. WHILE IN THE CLB AT APPROX FL240; THE R PACK TRIPPED OFF. ALL QRH PROCS WERE ACCOMPLISHED; A DSCNT WAS STARTED WITH COORD FROM ATC; OXYGEN MASKS WERE DROPPED AND A LEVELOFF WAS PERFORMED INITIALLY 17000 FT THEN 14000 FT. ADDITIONAL PROBS WERE HIGH TERRAIN IN THE AREA; WHICH WE DISCUSSED; AND DIFFICULTY IN RADIO COM WITH ATC. WE USED ACARS TO CALL DISPATCH; DISCUSSED ALL ITEMS WITH THE FLT ATTENDANTS AND LANDED UNEVENTFULLY. PLT INTERCOM WAS DIFFICULT WITH THE OXYGEN MASKS ON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE CREW REQUESTED DSCNT CLRNC VERY SHORTLY AFTER THE 'PACK TRIP' ANNUNCIATION. BECAUSE OF TERRAIN CLRNC; THE INITIAL DSCNT ALT WAS 17000 FT AND PRIOR TO REACHING 14000 FT; THE CABIN ALT WARNING HORN SOUNDED. THE CREW MANUALLY ACTIVATED THE MASK DROP BECAUSE THE CABIN WAS APCHING 12000 FT. THE RPTR STATED THE CREW'S MOST PRESSING PROB WAS COMS WITH ATC AND BTWN THEMSELVES WITH THE CREW OXYGEN MASKS ON. BECAUSE OF THE ALT AND NO REMOTE ANTENNAS IN THEIR AREA; AT 14000 FT AND BELOW THEY WERE FLYING UNDER THE MEA AND; THEREFORE; HAD LIMITED AND INTERMITTENT RADIO CONTACT. THE PLTS PUT THEIR MASKS ON TO BREATHE; BUT REMOVED THEM TO TALK TO ONE ANOTHER. THE RPTR ALSO STATED HE PERSONALLY REACTED TO ACTIVATING THE PAX'S OXYGEN MASKS BECAUSE OF HIS BELIEF THAT THE SIT WAS SERIOUS ENOUGH TO WARRANT IT. IN HIS MIND THERE WAS THE THOUGHT ABOUT BEING QUESTIONED OR SECOND-GUESSED THAT THE ACTION TAKEN WAS INCORRECT.