What was found
(CAN) AT 8000FT IN CLIMB OUT OF XXX THE FLIGHT CREW NOTICED THE CABIN ALTITUDE CLIMBING AT THE SAME RATE AS THE AIRCRAFT. CREW CARRIED OUT TROUBLESHOOTING OF PRESSURIZATION SYSTEM BUT COULD NOT RESOLVE THE ISSUE AND CALLED TOWER FOR RETURN. CABIN DID NOT REACH A HIGH ENOUGH ALTITUDE TO TRIGGER A CABIN ALT WARNING, NO MASKS DEPLOYED. GROUND CHECKS OF THE PRESSURIZATION CONFIRMED THAT THE SYSTEM WAS NOT WORKING. FAULT WAS TRACED TO THE SOLENOID VALVE IN THE CABIN SAFETY VALVE VACUUM LINE, THE SOLENOID HAD FAILED OPEN SO THE SAFETY VALVE WOULD NOT CLOSE. VALVE WAS REPLACED AND THE SYSTEM FUNCTION CHECKED SATISFACTORILY. VALVE P/N IS 101-380021-3. (TC# 20190328017)