Date: 201310
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Regional Jet 200 ER/LR (CRJ200)
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Climb
Airspace: Class E ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Pressurization Control System
Component problem: Design; Malfunctioning
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown; Situational Awareness; Confusion
Anomaly: Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Other / Unknown; Inflight Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Returned To Departure Airport; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: MEL; Human Factors; Aircraft; Procedure
Primary problem: Human Factors

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.

Callback: Reporter stated the Inboard and Overboard Avionics Cooling Exhaust valves are located in the Avionics Bay on the CRJ-200 aircraft. The Overboard cooling valve is suppose to 'Close' and the Inboard valve is suppose to 'Open' via proximity sensors when the Passenger Door is closed. Reporter stated flight crews are unaware the aircraft will not pressurize because the EICAS System does not indicate the Inboard and Overboard valves are not in the correct positions. The System doesn't differentiate if the valves are incorrectly positioned. The First Officer noticed the 'CABIN ALT' caution message on EICAS and the high cabin climb rate; but no EICAS INBD COOL or OVBD COOL caution messages. The Overboard Exhaust valve can be deferred in the 'Open' position; but the aircraft has to be flown unpressurized.



Synopsis: 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.