A B727-200 FLT DEPARTS MSY WITH THE L AIR CONDITIONING PACK MEL'ED. PLAN WAS TO FLY AT FL240 FOR DEST ARPT. FLT ENDS UP TOTALLY REPRESSURIZED AND DIVERTING TO DFW; TX.

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WE WERE DISPATCHED TO FL240 DUE TO THE R AIR CONDITIONING PACK BEING INOP FOR SEVERAL MAINT CARRY-OVERS. WE PLANNED; WITH THE DISPATCHER'S APPROVAL; TO TRY FOR FL240 AND USE A LOWER ALT IF NECESSARY; WHERE THE L AIR CONDITIONING PACK COULD MAINTAIN CABIN PRESSURE. FROM THE PREVIOUS FLT; DOUBTS EXISTED CONCERNING THE CAPACITY OF THE L AIR CONDITIONING PACK. PUSHBACK; START; TAXI AND TKOF WERE NORMAL. DURING CLBOUT; PASSING FL220; IT BECAME APPARENT THAT THE L PACK WOULD BE UNABLE TO MAINTAIN CABIN ALT BELOW 10000 FT. WE REQUESTED AND RECEIVED CLRNC IN STEPS DOWN TO FL200; FL180; 16000 FT; 14000 FT; 12000 FT; 11000 FT; AND FINALLY 10000 FT WHERE THE CABIN FINALLY STABILIZED WITH THE ACFT BEING VIRTUALLY UNPRESSURIZED. BOTH OUTFLOW VALVES WERE CLOSED MANUALLY DURING THE EVOLUTION; TO NO AVAIL. FOLLOWING A DECISION TO DIVERT TO A CLOSE HUB/MAINT BASE; AN OVERWT LNDG WAS UNEVENTFULLY ACCOMPLISHED; FOLLOWED BY AN EQUIP SWAP AND SUCCESSFUL COMPLETION OF THE FLT. SUPPLEMENTAL INFO FROM ACN 475772: WE WERE DISPATCHED FROM MSY TO SLC AT FL240 DUE TO THE R PACK BEING INOP FOR SEVERAL MAINT CARRY-OVERS. ONE OF THE MAINT CARRY-OVERS WAS DETECTED ENRTE TO MSY FROM ATL; AIR MIX VALVE INOP. THE PROC REQUIRED THAT WE TURN THE R PACK OFF AND CONTINUE TO MSY ON A SINGLE PACK. WHEN THIS WAS ATTEMPTED THE CABIN PRESSURE STARTED TO CLB SLOWLY. DUE TO THE FACT THAT WE WERE AT ALT WE ELECTED TO TURN IT BACK ON AND MONITOR IT CLOSELY. THE FLT INTO MSY WAS OTHERWISE UNEVENTFUL. AFTER LNDG AT MSY THE CAPT TALKED TO THE DISPATCHER AND AGREED THAT WE COULD STOP FOR FUEL ENRTE TO ZLC IF WE WERE UNABLE TO MAINTAIN CABIN PRESSURE AT FL240. CABIN ALT EXCEEDED 10000 FT MSL FOR A SHORT TIME AND MAY HAVE REACHED 11000 FT UNTIL WE DETERMINED THAT WE WERE NOT GOING TO REGAIN CABIN PRESSURE AT ALL. ALL APPLICABLE PROCS WERE FOLLOWED. OXYGEN MASKS WERE USED AND THE CARGO HEAT OUTFLOW VALVE AND MAIN OUTFLOW VALVES WERE MANUALLY CLOSED. WE DIVERTED INTO DFW WITH CONCURRENCE OF MAINT CTL AND THE DISPATCHER WHO CAME UP WITH DFW WX AND OVERWT LNDG DATA ESTIMATES.