A319
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 122; Flight Crew Type 7936
Aircraft Equipment Problem Less Severe
Flight Crew Diverted; Flight Crew Landed As Precaution; General Maintenance Action; General Flight Cancelled / Delayed
Aircraft
Pack 1 deferred inoperative.On climb out aircraft could not pressurize to maintain a normal cabin altitude. Received cabin altitude ECAM. Initiated a descent from FL275 to return cabin altitude below 10;000 ft. Flight Crew went on O2. Got vectors for an approach. Highest observed cabin altitude 13;900 ft. Notified F/As and asked them to make a diversion announcement. In IMC conditions during descent from 16;000 ft. to 1;500 ft. agl. Approach and landing uneventful.On climb out we got an indication of an unusual cabin altitude with a flashing cabin altitude indication on the lower ECAM passing approximately FL260. We looked for unusual configuration that might have caused the indication. We initially asked ATC to level off and then asked for a descent to FL180. Flight crew donned O2 masks.The cabin altitude continued to climb and we got a Cabin Altitude ECAM.  Asked ATC for clearance to descend to MEA of 13;400 ft. Notified F/As of problem and asked them to make an announcement of diversion into [an alternate airport]. F/As reported feeling a little lightheaded. Most of our communication was through Senior Attendants in the back of the airplane. Descended into IMC conditions and asked Center to verify MEA altitudes and altimeter setting. IMC conditions from 16;000 ft. through 1500 ft. Requested radar vectors to an ILS approach. Approach and landing were uneventful.The highest aircraft altitude was FL275 and the highest observed cabin altitude was 13;900 ft. The oxygen masks in the back of [the] aircraft did not deploy. No passengers complained of any issues other than the aircraft being warm. With the malfunction that caused the cabin pressurization problem; we also lost control of aircraft temperature. Highest cabin temperature 92 degrees.We deplaned passengers after conferring with station operations. Conducted an extensive debrief with [Maintenance]; who completed the write up. Maintenance troubleshooting uncovered a loose clamp on Pack 2 ducting. Flew the aircraft [after repairs] without incident or further problem.
A319 Captain reported diverting to an alternate airport after experiencing difficulty maintaining cabin pressure.