Narrative:

During preflight; we noticed that the right pack temperature controller did not work. Talked to dispatch and maintenance and we deferred the pack and got a new release for FL250 (original FL290) and new maintenance release. After takeoff per checklist; I checked the cabin pressure and saw that it was working normally. At a little more than 3;000 ft AGL the cabin was much higher but I don't know exactly how much. We did not feel any changes in cabin pressure. At FL250 the cabin warning horn went off. We put on oxygen masks and established communication. Pulled out the quick reference checklist and started running the checklist. At the same time; I asked for a descent to lower altitude. ATC was unclear what I was asking for; so I asked for an 'emergency descent' due to pressure problem. The quick reference checklist tells you to make sure the engine bleeds are on and then put both packs in high. As soon as the right pack was put into high; we started to get pressure and could feel it building in our ears. (The right pack was inoperative due to temperature control and was still able to push air.) the cabin altitude was coming down so we asked to stop our descent at 15;000 ft. At this point; the cabin altitude was about normal. The flight attendants called from the back and said they felt their ears popping. This was when we told them about the problem and said everything is now under control. The next ATC center asked if we still needed special handling and we told them no. From my seat looking at the cabin pressure; it looked like the cabin altitude never got above 11;000 ft.

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Original NASA ASRS Text

Title: A B737 with one pack inoperative and cruising at FL250 had the cabin altitude warning horn sound. An emergency was declared with a descent to 15;000 FT where cabin pressurization control was regained when the operating pack was place in high.

Narrative: During preflight; we noticed that the right pack temperature controller did not work. Talked to Dispatch and Maintenance and we deferred the pack and got a new release for FL250 (original FL290) and new Maintenance Release. After takeoff per checklist; I checked the cabin pressure and saw that it was working normally. At a little more than 3;000 FT AGL the cabin was much higher but I don't know exactly how much. We did not feel any changes in cabin pressure. At FL250 the cabin warning horn went off. We put on oxygen masks and established communication. Pulled out the Quick Reference Checklist and started running the checklist. At the same time; I asked for a descent to lower altitude. ATC was unclear what I was asking for; so I asked for an 'emergency descent' due to pressure problem. The Quick Reference Checklist tells you to make sure the engine bleeds are on and then put both packs in high. As soon as the right pack was put into high; we started to get pressure and could feel it building in our ears. (The right pack was inoperative due to temperature control and was still able to push air.) The cabin altitude was coming down so we asked to stop our descent at 15;000 FT. At this point; the cabin altitude was about normal. The Flight Attendants called from the back and said they felt their ears popping. This was when we told them about the problem and said everything is now under control. The next ATC Center asked if we still needed special handling and we told them no. From my seat looking at the cabin pressure; it looked like the cabin altitude never got above 11;000 FT.

Data retrieved from NASA's ASRS site as of April 2012 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.