What was found
WHILE ENROUTE FROM PHX TO RNO AIRCRAFT EXPERIENCED A CABIN PRESSURE CONTROLLER (CPC) SYSTEM NR 1 FAULT AND A FLUCTUATION OF PLUS OR MINUS 2000 FEET PER MINUTE OPERATION IN MANUAL MODE. ON THE PREVIOUS FLIGHT CPC SYSTEM NR 2 WAS PLACED ON MEL 21-31-01 CONDITION 1 FOR AUTO CABIN PRESSURE CONTROLLER SYSTEM NR 2 INOPERATIVE, AIRCRAFT DIVERTED TO LAS FOR REPAIRS. IN LAS MAINTENANCE TROUBLESHOT AND REPLACED THE OUTFLOW VALVE AND CLEARED MEL 21-31-01 IAW T/C R2D21301, OPERATIONAL CHECKOUT OF PRESSURIZATION SYSTEM WAS GOOD.