Narrative:

Inbound to ZZZ airport during descent, cabin altitude would climb with thrust levers at idle. Autopressurization was MEL'ed by maintenance. Manual pressurization was required and was performing throughout climb out and to cruise altitude. Established at cruise, cabin was at 8000 ft and was still climbing at 200 FPM. Left and right pack pressures were normal, but left pack was greater than 150 degrees temperature, while right pack temperature was below 30 degrees. Attempts to balance the temperature to more normal temperatures were not successful, in either the automatic or manual temperature control modes. Eventually the right pack shut down and we requested lower altitude. ATC gave us FL260, passing FL290 the left pack shut down. We donned our oxygen masks. I flew and handled the radio with ATC while the captain performed the red border checklist and company procedures. We declared an emergency, requested a lower altitude due to loss of pressurization and radar vectors to return to ZZZ1 airport. ZZZ1 center cleared us to FL240 and I restated we needed lower. ZZZ1 center stated that FL240 was all we could get now. Before I could respond, another aircraft told ZZZ1 center that I had declared an emergency, at which time ZZZ1 center cleared us to 10000 ft and a heading for ZZZ1 airport. At 10000 ft we removed our masks, opened the ram air to cool the cabin, ran all checklists to prepare for landing. In hindsight, we should have refused to take the aircraft once the autopressurization was MEL'ed. Callback conversation with reporter revealed the following information: the reporter stated on the ground in ZZZ that maintenance found the right air conditioning pack air cycle machine inlet and outlet ducting not connected. The reporter said the airplane automatic pressuriazation system was deferred prior to this trip. The reporter stated maintenance had worked on the right pack and apparently never finished the job.

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Original NASA ASRS Text

Title: A DC9-30 IN CRUISE AT FL330 DECLARED AN EMER AND DIVERTED DUE TO LOSS OF CABIN PRESSURIZATION CAUSED BY R AIR CYCLE MACHINE DUCT SEPARATION.

Narrative: INBOUND TO ZZZ ARPT DURING DSCNT, CABIN ALT WOULD CLB WITH THRUST LEVERS AT IDLE. AUTOPRESSURIZATION WAS MEL'ED BY MAINT. MANUAL PRESSURIZATION WAS REQUIRED AND WAS PERFORMING THROUGHOUT CLBOUT AND TO CRUISE ALT. ESTABLISHED AT CRUISE, CABIN WAS AT 8000 FT AND WAS STILL CLBING AT 200 FPM. L AND R PACK PRESSURES WERE NORMAL, BUT L PACK WAS GREATER THAN 150 DEGS TEMP, WHILE R PACK TEMP WAS BELOW 30 DEGS. ATTEMPTS TO BAL THE TEMP TO MORE NORMAL TEMPS WERE NOT SUCCESSFUL, IN EITHER THE AUTO OR MANUAL TEMP CTL MODES. EVENTUALLY THE R PACK SHUT DOWN AND WE REQUESTED LOWER ALT. ATC GAVE US FL260, PASSING FL290 THE L PACK SHUT DOWN. WE DONNED OUR OXYGEN MASKS. I FLEW AND HANDLED THE RADIO WITH ATC WHILE THE CAPT PERFORMED THE RED BORDER CHKLIST AND COMPANY PROCS. WE DECLARED AN EMER, REQUESTED A LOWER ALT DUE TO LOSS OF PRESSURIZATION AND RADAR VECTORS TO RETURN TO ZZZ1 ARPT. ZZZ1 CTR CLRED US TO FL240 AND I RESTATED WE NEEDED LOWER. ZZZ1 CTR STATED THAT FL240 WAS ALL WE COULD GET NOW. BEFORE I COULD RESPOND, ANOTHER ACFT TOLD ZZZ1 CTR THAT I HAD DECLARED AN EMER, AT WHICH TIME ZZZ1 CTR CLRED US TO 10000 FT AND A HDG FOR ZZZ1 ARPT. AT 10000 FT WE REMOVED OUR MASKS, OPENED THE RAM AIR TO COOL THE CABIN, RAN ALL CHKLISTS TO PREPARE FOR LNDG. IN HINDSIGHT, WE SHOULD HAVE REFUSED TO TAKE THE ACFT ONCE THE AUTOPRESSURIZATION WAS MEL'ED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED ON THE GND IN ZZZ THAT MAINT FOUND THE R AIR CONDITIONING PACK AIR CYCLE MACHINE INLET AND OUTLET DUCTING NOT CONNECTED. THE RPTR SAID THE AIRPLANE AUTO PRESSURIAZATION SYSTEM WAS DEFERRED PRIOR TO THIS TRIP. THE RPTR STATED MAINT HAD WORKED ON THE R PACK AND APPARENTLY NEVER FINISHED THE JOB.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.