Narrative:

Pack 2 was meled. My first officer (first officer) and I found it difficult to maintain temperature in the airplane while at altitude. We didn't think much of it because one pack was inoperative. We landed the airplane [at the destination] without incident. With a new first officer; we continued with [the next] flight. On this flight it was even more difficult to maintain comfortable temperatures in the cabin; while cruising at FL300 I noticed the [outflow valve] closed on the ecs (environmental control system) page. Instinctively I looked at the EICAS to see if there was anything abnormal with the pressurization as a result of the [outflow valve] closing. My first officer and I noticed the cabin altitude rapidly rising. By then we pulled the [emergency procedures checklist] to implement a plan of action and ensure that we are both familiar with the procedures. Cabin altitude continued to rise to 9;000 ft and was now in the caution range; then to 10;000 ft at which we got the cabin alert and EICAS indication. Both my first officer and I donned our O2 masks and proceeded with the cabin altitude hi item. I [advised ATC] and immediately started a descent per the [procedure]. We then continued with the QRH. Being concerned with passenger safety; I turned the knob to override the passenger O2 selector to ensure that the passengers had access to oxygen. Upon concluding the QRH and stabilizing the aircraft we decided to divert and landed with no further incident.while communicating with maintenance control; it was determined that the aircraft was previously written up due to pack 1 only blowing cold air. A sensor was replaced but then the #2 pack was meled. Per the MEL; both ram air vents were to be wired in the open position but only 1 was noticed to be so. In hindsight I should have simply flown at 10;000 ft back to [the departure airport].

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Original NASA ASRS Text

Title: ERJ-175 Captain reported diverting after experiencing a loss of cabin pressure.

Narrative: Pack 2 was MELed. My FO (First Officer) and I found it difficult to maintain temperature in the airplane while at altitude. We didn't think much of it because one pack was inoperative. We landed the airplane [at the destination] without incident. With a new FO; we continued with [the next] flight. On this flight it was even more difficult to maintain comfortable temperatures in the cabin; while cruising at FL300 I noticed the [outflow valve] closed on the ECS (Environmental Control System) page. Instinctively I looked at the EICAS to see if there was anything abnormal with the pressurization as a result of the [outflow valve] closing. My FO and I noticed the CABIN ALT rapidly rising. By then we pulled the [Emergency Procedures Checklist] to implement a plan of action and ensure that we are both familiar with the procedures. CABIN ALT continued to rise to 9;000 ft and was now in the caution range; then to 10;000 ft at which we got the cabin alert and EICAS indication. Both my FO and I donned our O2 masks and proceeded with the CABIN ALT HI item. I [advised ATC] and immediately started a descent per the [procedure]. We then continued with the QRH. Being concerned with passenger safety; I turned the knob to override the passenger O2 selector to ensure that the passengers had access to oxygen. Upon concluding the QRH and stabilizing the aircraft we decided to divert and landed with no further incident.While communicating with Maintenance Control; it was determined that the aircraft was previously written up due to Pack 1 only blowing cold air. A sensor was replaced but then the #2 Pack was MELed. Per the MEL; both RAM air vents were to be wired in the open position but only 1 was noticed to be so. In hindsight I should have simply flown at 10;000 ft back to [the departure airport].

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.