What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED AND THE AIRCRAFT RETURNED TO PHX DUE TO THE FLIGHT CREW REPORTING AT 14K PACK OUTPUT WAS AROUND 10C IN ALL ZONES AND CABIN TEMPS WERE 95-100 DEGREES. FLIGHT DECK HAD ZERO AIRFLOW FELT LIKE 120 DEGREES AND SUFFOCATING. CABIN WAS DESCRIBED AS EXTREMELY COLD WITH ICE PARTICLES FALLING AND SOUNDED LIKE A WINDOW WAS OPEN. THE AIRCRAFT LANDED SAFELY AT PHX WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED TRIM AIR PRESSURE VALVE 14HK PER AMM 21-63-52 AND ACCOMPLISHED A SATISFACTORY LEAK / OPERATIONAL CHECK WITH NO FAULTS NOTED.