What was found
ON DESCENT WITH ENG & WG ANTI-ICE ON, GOT NUMEROUS LVL 1 & 2 ALERTS FOR AIR SYS PROBLEMS. WITH CABIN ALT RISING, DID A HIGH SPEED DIVE TO 10,000 FT. CABIN ALT GOT TO 7800 FT & STARTED BACK DOWN TO NORMAL. VALUES OF CABIN ALT, THEREAFTER ALERTS INCLUDED LVL 2 FOR CABIN IN FLO, LVL 1 ALERTS FOR AIR SYS 1 OFF & AIR SYS 2 OFF. RAN ALL APPROP QRH PROCEDURES. FOUND 1-2 ISOL VLV HAD CLOSED ITSELF, NR 1 PACK TURNED ITSELF OFF & LOST NR 2 PACK WITH NO AIR SUPPLY. OPENED 1-3 ISOL & TURNED NR 1 PACK BACK ON. NR 3 AIR CONDITIONING PACK & NR 2 PNEUMATIC SYS WERE DEFERRED AT TIME OF EVENT, FOUND FAN AIR VLV FAULTY. R & R NR 1 FAN AIR VLV. R & R NR 1 PNEUMATIC SYS CONTROLLER. CONTROLLER OPERATIONS CHECKED GOOD. NR 1 FAN AIR VLV OPERATIONS CHECKED OK.