As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB NOTICED COCKPIT VERY WARM TO HOT. BETWEEN 12000' AND 18000' IT APPEARED A THIN LAYER OF SMOKE WAS PRESENT IN THE COCKPIT. ABOUT 30 SECONDS LATER THE FIRST OFFICER VERIFIED THERE WAS SMOKE IN THE COCKPIT AND THICKER. EMERGENCY DESCENT AND LANDING AT DEPARTURE POINT. FOUND EXCESSIVE AMOUNTS OF CARPET FIBERS TRAPPED IN FAN ON TEMPERATURE SENSING UNIT FOR COCKPIT. CLEANED FAN, OPERATION CHECKED GOOD.