What was found
CONT CABIN ZONE TEMP LIGHT ILLUMINATED. CLEARS WITH MASTER CAUTION RESET. GROUNDED - YES. PERFORMED PACK/ZONE TEMPERATURE CONTROLLER BITE TEST IAW B737-800 AMM 21-61-00-700-806-002. FOUND FLT DECK TRIM VALVE LIGHT ON IN HISTORY. VERIFY PASSED GREEN AND RESET. PACK OPERATE NORMALLY AND TRIM VALVE MOVES FREELY. FOUND TEMPERATURE BULBS IN FLIGHT DECK COMPLETELY COVERED IN DUST AND INSULATED. FILTER WAS ALSO VERY DIRTY. REPLACED FLIGHT DECK TEMP FILTER AND CLEANED TEMP BULBS.