What was found
PHX FLT 700 EN ROUTE PHX TO PHL. AT APPROXIMATELY 100 MILES EAST OF ABQ, AT FL310, THE CABIN ALTITUDE HAD CLIMBED TO 13,000 FT. THE CREW REPORTED A PACK ONE FAULT WITH THE NUMBER TWO PACK ON MEL AT THE TIME. THE FLIGHT DESCENDED TO 10,000 FEET AND RETURNED TO FIELD PHX WITHOUT FURTHER INCIDENT. MAINTENANCE FOUND NO PACK OR BLEED FAULTS ON THE POST FLIGHT REPORT. PERFORMED A BITE CHECK OF THE CABIN PRESSURE CONTROLLER AND TEMPERATURE CONTROLLER. NO FAULTS FOUND. RAN BOTH ENGINES WITH BLEED AND PACK INDICATION NORMAL. AIRCRAFT OK FOR SERVICE.