As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DIFFICULT TO CONTROL TEMP IN COCKPIT. MIX VALVE SHOWS FULL WARM WITH COLD AIR STILL BLOWING. FLT DECK TRIM VLV SHOWS WARM, BUT COLD AIR IS COMING IN, CREW CYCLED MASTER TRIM VLV AND OPERATED FLT DECK TRIM VLV IN MANUAL, NO HELP. REPLACED TRIM AIR VALVE.