What was found
DURING T/O A HEAVY ODOR SIMILAR TO MELTING PLASTIC COMING FROM PAX COMPT AT TIME OF DISCOVERY, TEMP CONTROL WAS SET ON AUTO, TEMP KNOB IN HOT POSITION. CREW DONNED THEIR OXYGEN MASKS & TURNED OFF ALL CABIN HEAT. APPROX 10 MINS ODOR DISSIPATED. A NORMAL LANDING. MX INSPECTED CABIN TEMP CONTROL VALVES FOR PROPER OPERATION & LEAKS, AND CHECKED TEMP SENSOR RESISTANCE. NO DEFECTS NOTED. AFTER CLEANING CABIN TEMP SENSOR, AND OPERATIONALLY CHECKING TEMP CONTROLS, AFT HEAT VENT WAS FOUND TO BE VERY HOT. BEECHCRAFT SB 21-3289 FOR REDUCING HEAT VENT TEMPERATURE INSTALLED USING KIT 128-5043-1. OPS CHECKS AFTER KIT INSTALLATION WERE GOOD. A/C WAS RETURNED TO SERVICE.