Narrative:

The aircraft was dispatched with 1 pack. At the top of climb when the power came back; the flow light came on. The cabin started climbing from 4000 ft at about 400 FPM. We followed the checklist; declared an emergency; and returned to ZZZ. Prior to dispatching from ZZZ the mechanics had to work on a problem with the good pack. When you are down to 1 pack; you should never dispatch with a pack that needed to be worked on. Callback conversation with reporter revealed the following information: reporter stated that he has received no further information about the incident. At the time of the event; maintenance stated that the water separator bag was frozen but the reporter stated the conditions allowing freezing to occur were not present.

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Original NASA ASRS Text

Title: AN MD80 DISPATCHED WITH 1 PACK INOP DECLARED AN EMER AND RETURNED TO LAND WHEN THE CABIN BEGAN CLBING UNCTLABLY AT 400 FPM.

Narrative: THE ACFT WAS DISPATCHED WITH 1 PACK. AT THE TOP OF CLB WHEN THE PWR CAME BACK; THE FLOW LIGHT CAME ON. THE CABIN STARTED CLBING FROM 4000 FT AT ABOUT 400 FPM. WE FOLLOWED THE CHKLIST; DECLARED AN EMER; AND RETURNED TO ZZZ. PRIOR TO DISPATCHING FROM ZZZ THE MECHS HAD TO WORK ON A PROB WITH THE GOOD PACK. WHEN YOU ARE DOWN TO 1 PACK; YOU SHOULD NEVER DISPATCH WITH A PACK THAT NEEDED TO BE WORKED ON. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE HAS RECEIVED NO FURTHER INFO ABOUT THE INCIDENT. AT THE TIME OF THE EVENT; MAINT STATED THAT THE WATER SEPARATOR BAG WAS FROZEN BUT THE RPTR STATED THE CONDITIONS ALLOWING FREEZING TO OCCUR WERE NOT PRESENT.

Data retrieved from NASA's ASRS site as of January 2009 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.