Date: 201506
Location: ZZZ.Airport, US
Weather elements / visibility: Thunderstorm
Aircraft: A319
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization System
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Anomaly: Aircraft Equipment Problem Less Severe
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport

Narrative: Upon entering the cockpit; I couldn't help to notice that the environmental conditions were quite warm. The APU BLEED was servicing both PACKS; we were doing our best to keep the aircraft cool. The aircraft had an Avionics Equipment Ventilation Computer deferral; the MEL was understood & complied with (Inlet & Extract blower set to OVRD per the procedure). Prior to Taxi; we had both agreed to leave the APU BLEED ON in attempts to better service the PACKS (as opposed to IDLE ENG BLEED). The active runway was RWY XY; shortly after departure; we received vectors for weather (VCTS [in the vicinity thunderstorms] around the field). On the climb-out; I queried ATC's vectors (which had us fly back down south due to weather & traffic congestion). Approximately through 5;000 FT; the Climb check was completed and I secured the APU (Engine Bleeds now service PACKS). Shortly after; we received an AIR PACK 2 Fault. Captain commanded the flight controls & radios; I ran the ECAM. The ECAM was very brief; as workload permitted; I referenced the QRH & AOM for additional guidance. The APU at that time was still AVAIL; so we also cycled back to using the APU BLEED to attempt to alleviate the issue. We contacted Maintenance at Airport ZZZ and queried if there was any other guidance on the issue (as we were still within range to ZZZ). They advised to cycle PACK2 ON/OFF; if that didn't work to contact Maintenance Control. We received no other guidance from QRH/AOM/Maintenance than to leave PACK 2 in the OFF position if we could not cycle it to operate normally.As the issue progressed however; we tried AIRINC to contact Maintenance Control. We could not get a word-in as the frequency was already very busy. At this point; I resumed communications of COM1 & PM duties; we were still on vectors for weather and climbing through FL240. We continued to monitor the performance of our remaining PACK in the climbout. We noticed that the Cabin Altitude at FL250 was over 7;000 FT and considered a reduction in the rate of climb to help facilitate effective pressurization. We received an APU BLEED Fault ECAM and tried to communicate to ATC to stop our climb to work the issue. A few moments later; we received a CAB PR EXCESS CAB ALT ECAM. PF had controls & radios; I worked the ECAM; requiring us to don Oxygen masks and commence a Rapid Descent to 10;000 MSL or MEA (whichever is higher). ATC initially gave PF 11;000 FT Altitude to maintain; we requested lower and expedited down to 8;000 FT. During the process of working the ECAM; we reached a CAB ALT of approximately 9;700 FT. As the Aircraft descended; so did the Cabin Alt. We promptly [notified ATC] and requested vectors back to ZZZ. As we were descending through 10;000 FT; I resumed my PM duties and helped activate the approach; obtain the latest ATIS; get Direct ZZZ and Captain briefed the Arrival. No further issues arose and we made a Normal Visual approach and landing.Typically our SOP's have us shutdown the APU after engine start; we elected to leave it on in hopes it would do a better job cooling the cabin than Idle Thrust from the Engines during taxi. Inflight; without further guidance other than simply turning OFF PACK 2 and having only PACK 1 supply pressurization to the cabin; we queried the effect this would have on the aircraft with the Avionics Equip MEL and tried both bleed sources that we had (Engine & APU) in attempts to maintain a regular Cabin Alt rate of climb.




Synopsis: A319 flight crew experienced pressurization problem and returned to departure airport.