What was found
ON RECALL OF MASTER CAUTION SYSTEM, ZONE TEMP LIGHT ILLUMINATED ON CONT CAB. EXTINGUISHED DURING MASTER CAUTION RECALL. GROUNDED-YES. PERFORMED NR 2 PZTC BITE, REF B737-800 AMM 21-61-00. FOUND FLT DECK TRIM VALVE FAIL IN BIT, PREV FLT AND VERIFY (MULTIPLE ATTEMPTS). REMOVED AND REPLACED FLT DECK ZONE TRIM AIR MODULATING VALVE, REF AMM 21-61-21. PZTC BITE TEST PASS BIT, PREV FLT AND VERIFY VALVE REPLACEMENT AND RESET. PERFORMED CABIN TEMP CONTROL AND INDICATION OPERATIONAL TEST, REF AMM 21-61-00. OPERATIONS CHECKS GOOD, NO FAULTS. ETOPS SIGNIFICANT SYSTEM GROUND VERIFICATION SUCCESSFUL.