What was found
MCO - FLT 808 - CLIMBING THROUGH FL270, THE CABIN ALTITUDE WARNING HORN SOUNDED. CABIN ALTITUDE WAS AT 11,000 FEET AND CLIMBED AS HIGH AS 13,000 FEET. EMERGENCY DESCENT WS MADE TO 10,000 FEET. FLIGHT RETURNED TO FIELD TO MCO AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REMOVED AND REPLACED THE LEFT AIR CYCLE MACHINE AND THE LEFT 35 DEGREE TEMPERATURE CONTROL BOX. OPERATIONAL CHECK AND PRESSURIZATION CHECK GOOD. NO LEAKS NOTED. (M)