What was found
PASSING FL280 IN CLIMB CABIN ALT ALERT CLIMBING THROUGH 9000', STARTED DESCENT AS CABIN 10,000. DECLARED EMERGENCY FOR DESCENT, NO PASSENGER MASKS, NO OVERWEIGHT LANDING AT 141,800 LBS. CREW VERBALLY REPORTED THAT THEIR CABIN PRESSURE PAGE SHOWED SKIN AIR VALVE, EXTRACT AND SAFETY VALVE ALL INDICATED CLOSED. PACK 1 FLOW CONTROL VALVE IS STUCK IN OPEN POSITION. THE AIRCRAFT WAS GROUNDED. REPLACED LEFT HAND PACK CONTROL VALVE PER AMM 21-51-51.