What was found
ON RECALL, CONT CAB ZONE TEMP LIGHT CAME ON. GROUNDED - YES. OPERATED R & L PACK SYSTEMS = CONT CAB ZONE TEMP LIGHT NOT ON AND NOT ILLUMINATED ON RECALL. BITE TEST OF #2 PZTC FAULTED FLT DECK TRIM VALVE ON PREVIOUS FLIGHTS & PZTC #1 FAULTED TCV THIS PACK, BOTH FAULTS CLEARED ON GREEN GO LIGHT ILLUMINATED. GVI OF CONT CABIN TEMP SENSOR & FAN = MOSTLY COVERED IN FUZZ / DUST WITH VERY LITTLE AIRFLOW, CLEANED FAN AND TEMP SENSOR. OPERATED R & L PACK SYSTEMS AGAIN AND ALL ZONE TEMP CONTROLS OPERATE APPROPRIATELY WITH NO FAULTS NOTED ON #1 & #2 PZTC BITE TEST. REF B737-800 FIM 21-62 TASKS 842 & 801, & B737-800 AMM 21-61-10.