As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIR RETURNED DUE TO AIR CONDITIONING FAIL LIGHT ILLUMINATED AND CABIN REVERTED TO EMERGENCY PRESSURIZATION MODE. AIRCRAFT ISSUED SPECIAL FLIGHT PERMIT, FOR MAINTENANE AT SERVICE CENTER. MAINTENANCE FOUND THE CABIN TEMPERATURE CONTROL VALVE TO BE DEFECTIVE. REPLACED SAME AND FUNCTIONALLY TESTED SATISFACTORY. AIRCRAFT RETURNED TO SERVICE. (EA25200509515) (K)