As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHX-SNA - FLT 661 - AIR TURNBACK, CREW UNABLE TO PRESSURIZE AIRCRAFT ON CLIMB-OUT. AIRCRAFT RETURNED TO PHX AND LANDED WITHOUT FURTHER PROBLEMS. MAINTENANCE REMOVED AND REPLACED E/E COOLING VLV. OPS CHECK GOOD. AIRCRAFT RETURNED TO SERVICE. (M)