Narrative:

Upon initial climb from ZZZ; around 10;500 ft MSL; the pilot not flying noticed a high cabin climb rate. This was closely followed by a 'cabin altitude' caution message on EICAS. I leveled the airplane at 11;000 ft and asked ATC for a descent to 10;000 ft. We ran the QRH checklist for the cabin altitude message and attempted 'manual' pressurization; which did not work. Nothing was out of order that we could see; so I contacted ZZZ1 radio and could not make contact; presumably because of our altitude. I ACARS messaged dispatch that we could not pressurize the aircraft and would return to ZZZ. We eventually decided to depressurize the aircraft by checklist at a lower altitude and land unpressurized. We could not control the cabin in 'auto' or 'manual' modes at any time. We entered a holding pattern to burn fuel and completed a normal landing. Upon arrival back at ZZZ; local maintenance met the aircraft. They determined that the previous night; upon clearing the ovbd cool MEL deferral; the cables to the inboard cooling and overboard cooling valves were wired backwards. In other words; the cable meant for the overboard valve was connected to the inboard valve; and vice-versa. They corrected the problem; checked the aircraft pressurization and we were re-dispatched to ZZZ2. The biggest threat from this maintenance error is that we did not have any indication that the valves were in the wrong position at any time; before or during the flight; and the aircraft would not pressurize. The errors were presumably made by maintenance at ZZZ and included connecting the valves backwards. Undesired aircraft states were not reached; however not having pressurization could be considered 'undesired'. I feel as a crew we performed well. There was no way we could have known about the incorrect valve position. I feel that maintenance at ZZZ should be well versed in this deferral; as it is fairly common on this type [of aircraft] . Additional measures might have prevented this. Those might include more robust operational checks regarding the institution and clearing of this particular deferral. The cables are apparently labeled; however the ability to connect the 'right cable to the wrong valve' is a threat. Perhaps the cannon plugs should be of different size; or color-coded. I'm not sure precisely what is involved in this deferral so I cannot comment further on the procedures that operator uses.

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Original NASA ASRS Text

Title: Pilot reports they could not control the cabin pressurization in the Auto or Manual mode during initial climb in a CRJ-200 aircraft; air turnback was accomplished. Maintenance later discovered the Inboard and Outboard Avionics Cooling Exhaust valve electrical connectors were previously crossed. No EICAS message of valve position faults.

Narrative: Upon initial climb from ZZZ; around 10;500 FT MSL; the pilot not flying noticed a high cabin climb rate. This was closely followed by a 'CABIN ALT' caution message on EICAS. I leveled the airplane at 11;000 FT and asked ATC for a descent to 10;000 FT. We ran the QRH checklist for the CABIN ALT message and attempted 'Manual' pressurization; which did not work. Nothing was out of order that we could see; so I contacted ZZZ1 Radio and could not make contact; presumably because of our altitude. I ACARS messaged Dispatch that we could not pressurize the aircraft and would return to ZZZ. We eventually decided to depressurize the aircraft by Checklist at a lower altitude and land unpressurized. We could not control the cabin in 'Auto' or 'Manual' modes at any time. We entered a holding pattern to burn fuel and completed a normal landing. Upon arrival back at ZZZ; local Maintenance met the aircraft. They determined that the previous night; upon clearing the OVBD COOL MEL deferral; the cables to the Inboard cooling and Overboard cooling valves were wired backwards. In other words; the cable meant for the overboard valve was connected to the inboard valve; and vice-versa. They corrected the problem; checked the aircraft pressurization and we were re-dispatched to ZZZ2. The biggest threat from this maintenance error is that we did not have any indication that the valves were in the wrong position at any time; before or during the flight; and the aircraft would not pressurize. The errors were presumably made by Maintenance at ZZZ and included connecting the valves backwards. Undesired aircraft states were not reached; however not having pressurization could be considered 'undesired'. I feel as a crew we performed well. There was no way we could have known about the incorrect valve position. I feel that Maintenance at ZZZ should be well versed in this deferral; as it is fairly common on this type [of aircraft] . Additional measures might have prevented this. Those might include more robust Operational Checks regarding the institution and clearing of this particular deferral. The cables are apparently labeled; however the ability to connect the 'right cable to the wrong valve' is a threat. Perhaps the cannon plugs should be of different size; or color-coded. I'm not sure precisely what is involved in this deferral so I cannot comment further on the procedures that operator uses.

Data retrieved from NASA's ASRS site as of July 2013 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.