What was found
AT F360 L BLEED DUCT WARNING AND LT BLEEDS CLOSED. THE RT SIDE PRSOV VALVE CLOSED ON ITS OWN. PERFORMED EMERGENCY DESCENT TO 10K FT CABIN ALTITUDE CLIMBED TO 12,500 FT BEFORE STABILIZING PRIOR TO 10K FT. PAX O2 MASKS WERE MANUALLY DEPLOYED. LT DUCT WARNING AND BLEED SHUTDOWN IN FLT. PERFORMED INSPECTIONS OF LEFT BLEED DUCTING AND LOOPS. R&R LT PRSOV IAW CRJ 900 AMM 36-12-01. OPS TEST AND LEAK CK GOOD ON LT PRSOV IAW CRJ 900 AMM 36-12-01, 36-10-00. P/N OFF GG670-80002-9 S/N 01290 P/N ON GG670-80002-7 S/N ON 00597. REMOVED RT SAFETY VALVE AND INSTALLED SERVICEABLE UNIT IAW CRJ 900 AMM 21-32-03-400-801 COMPLIED WITH OPS CHECK IAW CRJ 900 AMM 21-32-03-720-802. REQUIRED TEST FLIGHT SATISFACTORY.