What was found
DIVERSION/DECLARED EMERGENCY. AT CRUISE - FL370, EQUIPMENT COOLING OFF LIGHT CAME ON, IT WAS ALREADY IN ALT, CONTINUED. ALTITUDE WARNING HORN SOUNDED ABOUT 20 MINS LATER. STARTED EMERGENCY DESCENT, SWITCHED CONTROLLER TO ALT, CABIN RISE WENT FROM 200-300 CLIMB TO 0. HORN STOPPED AT FL180. REMOVED AND REPLACED CABIN PRESSURE CONTROLLER AND LOWER EXHAUST COOLING TEMPERATURE SENSOR PER AMM.