A B737-300 PIC ELECTS TO USE AN MEL'ED AIR CONDITIONING PACK WHEN THE REMAINING PACK IS NOT PRESSURIZING THE ACFT AT 9000 FT AFTER DEPARTING ELP; TX. ACR INSPECTOR ON BOARD.

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ON DEC/XA/99; WE BEGAN THE THIRD DAY OF A 4 DAY TRIP IN EL PASO; TX. OUR FIRST LEG WAS FROM ELP TO DFW DEPARTING AT AB45. WE BEGAN OUR PREFLT AT APPROX AB05 AND WERE TOLD THAT AN FAA SAFETY INSPECTOR WOULD BE WITH US ON THE LEG TO DFW. AS I DID THE WALKAROUND INSPECTION; I NOTICED THAT THE R-HAND RAM AIR DOOR WAS CLOSED (NOT NORMAL FOR GND OP). WHEN I CHKED THE ACFT LOGBOOK; THE CREW THAT BROUGHT THE ACFT IN THE PREVIOUS NIGHT HAD WRITTEN THE 'R-HAND RAM AIR DOOR AS BEING CLOSED ON THE GND' AND HAD GND CREW PLACARD THE R-HAND PACK INOP. DURING OUR COCKPIT PREFLT; WE DISCUSSED OP WITH THE L-HAND PACK AS INOP; AND FLT CTL FILED US AT AN ALT (FL240) WHICH WAS SAFE FOR 1 PACK OP. WE WERE ALSO WORKING ANOTHER UNRELATED MECHANICAL PROB WITH MAINT OVER THE TELEPHONE. TAXI AND TKOF WERE NORMAL EXCEPT FOR BEING ABOUT 25 MINS LATE. AS I WAS RUNNING THE AFTER TKOF CHKLIST; I NOTICED THAT THE L-HAND PACK WAS NOT PRESSURIZING THE ACFT. THE CABIN ALT WAS APPROX THE SAME ACFT ALT (8500 FT MSL). I TOLD THE FO TO LEVEL AT 10000 FT MSL. AT THIS POINT I HAD 2 OPTIONS: 1) RETURN TO ELP UNPRESSURIZED OR 2) SEE IF THE R-HAND PACK WOULD PRESSURIZE. I ELECTED TO GO WITH OPTION #2. IT PRESSURIZED THE ACFT. I LEFT THE APU RUNNING AS BACKUP AND WE CONTINUED TO DFW WITH NO FURTHER PROBS. SUPPLEMENTAL INFO FROM ACN 456530: MEL PROCS REQUIRE THE CREW TO CLOSE THE AIR CONDITIONING ISOLATION VALVE; KEEP THE AFFECTED PACK OFF FOR TKOF; AND PWR THE L PACK FROM THE APU WITH THE #1 ENG BLEED SWITCH OFF. THE L PACK APPEARED TO OPERATE NORMALLY. AFTER TKOF; WE AGAIN COMPLIED WITH MEL PROCS AND RECONFIGURED THE PNEUMATIC BLEEDS. CONFIRMING THAT ALL SWITCHES WERE PROPERLY CONFIGURED; AND RECOGNIZING THAT THE AIRPLANE WAS NOT PRESSURIZING; THE CAPT ELECTED TO TURN ON THE R PACK WITH THE L PACK STILL ON. UPON LNDG AT DFW; WE IMMEDIATELY TURNED OFF THE R-HAND PACK AND AGAIN CLOSED THE ISOLATION VALVE TO COMPLY WITH MEL PROCS.