B767-300 FLT CREW DISPUTES LOGIC OF DISPATCHING WITH AN MEL ITEM ON THE R PACK WHEN THE L PACK IS MEL'ED INOP.

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WE WERE DISPATCHED WITH THE FOLLOWING DEFERRED ITEMS: MEL APU DOOR OPEN; MEL L-HAND PACK INOP. DURING CLB AT FL280; THE R BLEED OVERHEAT EICAS MESSAGE DISPLAYED. R PACK OFF MESSAGE DISPLAYED. OXYGEN MASKS WERE DONNED AND QRH NON-NORMAL PROC ACCOMPLISHED FOR R-HAND BLEED OVERHEAT. BLEED WAS RESET ACCORDING TO QRH AND OPERATED NORMALLY FOR DURATION OF FLT TO PHX. THE CABIN DID NOT REACH 10000 FT. I ENTERED THE DISCREPANCY IN THE LOGBOOK AND MAINT DEFERRED THE R-HAND ENG HIGH STAGE BLEED AND THE R ENG THRUST REVERSER UNDER MEL'S. THESE MEL'S WERE NOT DISPLAYED ON OUR FLT PAPERWORK FOR THE NEXT FLT. WE LOOKED UP THE MEL'S IN THE MEL BOOK ON THE AIRPLANE AND DISCOVERED THAT MEL FOR HIGH STAGE BLEED HAD A NOTE THAT R BLEED OFF AND R PACK OFF MAY OCCUR AT CERTAIN PWR SETTINGS. THERE WAS A PROC DESCRIBED TO ELIMINATE THE BLEED AND PACK OFF MESSAGES WHICH INVOLVED CHKING THE DUCT PRESSURE AND SWITCH POS AND THEN ADDING PWR ON THAT ENG TO 80% N2 TO INCREASE AVAILABLE AIR. I DID NOT FEEL IT WAS SAFE TO OPERATE WITH THIS COMBINATION OF MEL ITEMS AT FL350. MY REASONING FOR THIS WAS THAT A LOSS OF PRESSURIZATION AT FL350 IS AN EMER WHICH REQUIRES IMMEDIATE ACTION BY THE CREW. I CONTACTED FLT CTL AND ADVISED THEM. THEY HAD ME SPEAK WITH MAINT CTL AND I ADVISED THEM. I THEN CALLED SYS OPS TO SEE IF THEY COULD HELP ME FIND A WAY TO OPERATE THE TRIP. I WAS EVENTUALLY CALLED BACK BY A MAINT CTLR. HE ADVISED ME ABOUT USING THE OTHER ENG'S BLEED SOURCE. WHILE I KNEW THIS WOULD WORK; IMPROVISING PROCS TO DISPATCH A FLT WAS QUESTIONABLE IN MY MIND. HE COULD NOT PROVIDE ME WITH A REF TO USE FOR THE PROC HE WAS DESCRIBING. WE SEARCHED OUR BOOKS FOR A WAY TO OPERATE WITH THE CONDITIONS WE HAD AN IN THE PACK OFF CHKLIST IN THE B767 QRH THE FO FOUND A REF TO USING AN ALTERNATE ENG BLEED SOURCE UNDER BOTH PACKS OFF. I CONTACTED FLT CTL AND ADVISED THEM WE COULD NOW DEPART.