B757 CABIN ALT EXCEEDS 10000 FT WHILE CLIMBING THROUGH FL340 ON ONE PACK. CARGO FLT CREW OBTAINS ATC CLRNC TO DESCEND FOR TROUBLESHOOTING; AND REGAINS PRESSURIZATION.

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WE WERE CLBING OUT OF ABOUT FL340 TO A FILED ALT OF FL390. THE FO WAS FLYING AND THE AUTOPLT WAS ENGAGED. THE CABIN ALT ALERT ILLUMINATED ALONG WITH THE AUDIO WARNING. WE CONFIRMED THAT THE CABIN ALT HAD EXCEEDED 10000 FT MSL AND WAS STILL CLBING. WE DONNED OXYGEN MASKS AND ADVISED ATC THAT WE HAD A PRESSURIZATION PROB AND WOULD HAVE TO DSND UNTIL WE COULD GET THE CABIN BELOW 10000 FT. ATC GAVE US A VECTOR OFF COURSE AND AN INITIAL DSCNT TO ABOUT FL230. SHORTLY AFTER THAT WE WERE GIVEN CLRNC TO DSND TO 11000 FT. AT THIS POINT; WE HAD RUN THE RECALL ITEMS AND GONE TO THE CABIN ALT CHKLIST IN THE QRH. THE OUTFLOW VALVE WAS ALREADY FULLY CLOSED. SHORTLY AFTER THE CABIN ALT WARNING AND DURING OUR DSCNT; WE GOT PRESSURIZATION 'AUTO 1' AND 'AUTO 2' MESSAGES. AS IS COMMON PRACTICE; AFTER DEP WE HAD TURNED OFF THE L PACK TO REDUCE COCKPIT NOISE. WHILE WE WERE DSNDING TO 11000 FT AND RUNNING THE CHKLISTS; I NOTICED THAT THE R ENG BLEED VALVE WAS OFF; ALTHOUGH THE BLEED SWITCH WAS ON. I NOW REALIZED THAT WE HAD LOST PRESSURIZATION BECAUSE NEITHER PACK WAS PRESSURIZING THE ACFT. I TURNED THE L PACK ON AND THE ACFT BEGAN TO PRESSURIZE; BUT THE AUTO PRESSURE CTLRS WERE STILL INOP. DURING THE DSCNT WE ESTABLISHED CONTACT WITH DISPATCH AND MAINT. I DESCRIBED THE PROB AND ADVISED MAINT THAT WE WERE WITHIN 100 MI OF PIE; MCO AND JAX. BY THIS TIME; WE HAD GOTTEN THE CABIN DOWN TO 8000 FT AND WERE ABLE TO REMOVE OUR OXYGEN MASKS. ALSO ABOUT THIS TIME; WHILE I WAS DISCUSSING THE PROB WITH MAINT; THE R ENG BLEED VALVE BEGAN TO FUNCTION. NO CORRECTIVE ACTION HAD BEEN TAKEN ON OUR PART. WE NOW HAD 2 BLEED SOURCES AND 2 PACKS. SHORTLY AFTER THIS HAPPENED WE GOT THE PRESSURIZATION AUTO CTLRS BACK. I ADVISED MAINT OF ALL THESE EVENTS AND THEY ASKED US TO PROCEED TO DEST. WE CLBED TO FL320 AND PROCEEDED TO DEST UNEVENTFULLY. THE DUCT PRESSURE; WITH THE ISOLATION VALVE CLOSED; WAS HIGH AT CLB AND CRUISE PWR ON BOTH SIDES OF THE MANIFOLD; OVER 60 PSI. THE NOISE LEVEL IN THE COCKPIT (DUAL OR SINGLE PACK OP) WAS ALSO HIGHER THAN USUAL. THE MAINT DISCREPANCIES WERE WRITTEN UP WITH CLARIFYING NOTES AND A CONTRACT MECH MET THE ACFT. WE ASSISTED HIM WITH AN ENG RUN TO PERFORM THE REQUIRED MAINT PROCS AND MAINT AUTH THE MECH TO CLR THE LOGBOOK ENTRIES. WHEN THE L PACK HAD BEEN INITIALLY TURNED OFF AFTER TKOF I HAD CLRED THE EICAS MESSAGES FOR THE L PACK AND THE L ENG BLEED 'OFF.' WHEN OPERATING IN THIS MODE IT IS NOT UNCOMMON FOR THE 'BLEED OFF' MESSAGE TO REAPPEAR. I SUSPECT THAT THIS HAD HAPPENED AND I DID NOT CLR THE 'BLEED OFF' MESSAGE IN A TIMELY MANNER. WE HAD ALSO BEEN USING CTR TANK FUEL AND THEN BALANCING THE WING FUEL AND THE FUEL PUMP MESSAGES HAD BEEN INTENTIONALLY LEFT ON THE SCREEN AS A REMINDER. ACCORDINGLY; WHEN THE R BLEED VALVE FAILED; NEITHER OF US NOTICED THAT ANOTHER EICAS MESSAGE HAD APPEARED UNTIL WE GOT THE CABIN ALT WARNING. INTERESTINGLY; THE RECIRCULATION FAN APPEARED TO KEEP THE CABIN TEMP COMFORTABLE DURING THE EVENT AND THE COCKPIT NOISE LEVEL DID NOT DROP ENOUGH FOR US TO NOTICE THE PROB PRIOR TO THE WARNING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT IT IS COMPANY PRACTICE TO OPERATE WITH 1 PACK -- BOTH PACKS ONLY REQUIRED DURING TKOF. APPARENTLY ACFT DUCTING ON COMPANY'S B757'S CREATES A NOISE LEVEL THAT CAN INTERFERE WITH COMMUNICATIONS UNLESS ONE PACK (NORMALLY THE LEFT) IS TURNED OFF.