What was found
EN ROUTE PDX-ORD, DURING CRUISE, CABIN GOT VERY COLD. BOTH PACK PRESSURES OK. CABIN STARTED CLIMBING, INITIATED EMERGENCY DESCENT. CABIN MASKS DEPLOYED AND SPENT. PACK PRESSURE INDICATED ZERO IN DESCENT. BELOW 10,000 FEET PACKS REINSTATED. LANDED ORD WITHOUT INCIDENT. REPLACED LEFT AND RIGHT WATER SEPARATOR TEMPERATURE CONTROL VALVES. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)