Narrative:

About 1hr 15min into the flight at FL330; the cabin pressurization controller began acting erratically. This was also accompanied with rapid pressure fluctuations that could be felt in the ears. The cabin altitude began climbing at an approximate rate of 1500 fpm initially and later would increase further. We initiated the procedure 'cabin pressure off schedule or erratic'. We selected the pressurization controller to stby with no change that corrected the problem. The outflow valve control wheel appeared to be sticking or stuck and every time the automatic system would recoil; the outflow valve would stick in a position more open than the last. We selected the system to manual and manually attempted to move (muscle) the control wheel forward to close the outflow valve. We were unsuccessful in being able to position the outflow valve in a closed position sufficient to maintain cabin pressure. While attempting to manually close the outflow valve we were approaching a cabin altitude of 9000-10000 ft. Prior to reaching step #3 on the QRH; the 'cabin altitude' master warning illuminated. We elected to stop performing the steps and performed the memory items required for a 'cabin altitude/ rapid depressurization' followed by 'rapid descent'. The first officer was PF with the autopilot on. We donned our oxygen masks and established communication with ATC. I took control of the aircraft; [advised ATC]; and initiated an emergency descent. During the descent while running the QRH; we ensured the blue 'cabin O2 on' was illuminated. We elected to turn towards and divert. When approaching 10000 ft we removed our oxygen masks; and I made a call to the flight attendant's and briefed them followed by a clear PA to the passengers stating what had happened; that we were at a safe altitude to remove oxygen masks; and that we were diverting.once below 10000 ft all operations/ communications were normal; as well as a normal landing. We contacted dispatch via [commercial radio] around 10000 ft to inform them of our situation. We taxied to the gate and deplaned. Passengers were in good spirits as they deplaned and no injuries were noted. Once on the ground; movement of the outflow valve was still restricted even with no air load on the valve. Two logbook entries were made. One for the loss of cabin pressure and one for 3 pob's that were used by the flight attendant's. All aircraft emergency equipment appeared to operate normally. The flight attendant's assisted a special needs passenger and an infant with the donning of their oxygen masks. After the flight deplaned; our flight attendant's went above and beyond the duty to assist a special needs teen to make accommodations to catch a flight later that night. Prior to our crew deplaning; we had a formal debrief as a crew in its entirety about the event.this aircraft had been recently painted. This aircraft had a similar problem before. They returned to the airport of origin when they were unable to pressurize. Ensure outflow valves (scoop) are painted properly (or not painted over at all).

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Original NASA ASRS Text

Title: MD-80 flight crew experienced a faulty pressurization controller and outflow valve. Flight diverted to enroute airport.

Narrative: About 1hr 15min into the flight at FL330; the cabin pressurization controller began acting erratically. This was also accompanied with rapid pressure fluctuations that could be felt in the ears. The cabin ALT began climbing at an approximate rate of 1500 fpm initially and later would increase further. We initiated the procedure 'Cabin Pressure off Schedule or Erratic'. We selected the pressurization controller to STBY with no change that corrected the problem. The outflow valve control wheel appeared to be sticking or stuck and every time the automatic system would recoil; the outflow valve would stick in a position more open than the last. We selected the system to manual and manually attempted to move (muscle) the control wheel forward to close the outflow valve. We were unsuccessful in being able to position the outflow valve in a closed position sufficient to maintain cabin pressure. While attempting to manually close the outflow valve we were approaching a cabin ALT of 9000-10000 ft. Prior to reaching step #3 on the QRH; the 'Cabin ALT' Master Warning illuminated. We elected to stop performing the steps and performed the memory items required for a 'Cabin ALT/ Rapid Depressurization' followed by 'Rapid Descent'. The FO was PF with the autopilot on. We donned our Oxygen masks and established communication with ATC. I took control of the aircraft; [advised ATC]; and initiated an emergency descent. During the descent while running the QRH; we ensured the blue 'Cabin O2 On' was illuminated. We elected to turn towards and divert. When approaching 10000 ft we removed our oxygen masks; and I made a call to the FA's and briefed them followed by a clear PA to the passengers stating what had happened; that we were at a safe altitude to remove oxygen masks; and that we were diverting.Once below 10000 ft all operations/ communications were normal; as well as a normal landing. We contacted dispatch via [commercial radio] around 10000 ft to inform them of our situation. We taxied to the gate and deplaned. Passengers were in good spirits as they deplaned and no injuries were noted. Once on the ground; movement of the outflow valve was still restricted even with no air load on the valve. Two logbook entries were made. One for the loss of cabin pressure and one for 3 POB's that were used by the FA's. All aircraft emergency equipment appeared to operate normally. The FA's assisted a special needs passenger and an infant with the donning of their oxygen masks. After the flight deplaned; our FA's went above and beyond the duty to assist a special needs teen to make accommodations to catch a Flight later that night. Prior to our crew deplaning; we had a formal debrief as a crew in its entirety about the event.This aircraft had been recently painted. This aircraft had a similar problem before. They returned to the airport of origin when they were unable to pressurize. Ensure outflow valves (scoop) are painted properly (or NOT painted over at all).

Data retrieved from NASA's ASRS site 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.