As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER ENGINE START, WE ESTABLISHED AIR CONDITIONING AND GOT THE CONT CABIN ZONE TEMP LIGHT RAN QRH AND THE LIGHT EXTINGUISHED WITH MASTER CAUTION RESET. GROUNDED - YES. TROUBLESHOT TO CONTROL CABIN TRIM VALVE. REMOVED AND REPLACED ZONE TRIM AIR MOD VALVE REF B737-800 AMM 21-61-21 OPS CHECK GOOD LEAK CHECK GOOD NO LIGHT ON.