What was found
PROBLEM DESCRIPTION: LEFT PACK TRIP OFF IN FLIGHT. UNABLE TO HOLD PRESSURIZATION AT FL 320, FL 270, FL 240 OR FL 210 UNTIL FL140. THERE WAS SOME PRESSURIZATION, AND THE CABIN ALTITUDE FINALLY WENT DOWN FROM 10000 FEET. REMOVED AND REPLACED 250 DEG TEMP SENSOR IAW B737 AMM 21-61-51. PERFORMED TEST OF DUCT OVERHEAT SWITCH, OPS CHECK GOOD. OPS CHECK IAW B737 AMM 21-00-00, NO DEFECTS NOTED.