As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE RUNNING APU ON THE GROUND WITH COCKPIT PAC ON HIGH GOT SMOKE IN COCKPIT. COCKPIT PAC SUPPLY TEMP ROSE RAPIDLY. COCKPIT PAC OIL RESEVOIR WAS CLEAR ON PREFLIGHT NOW BLACK. REPLACED COCKPIT PAC ACM & COALESCER SOCK OPS CK GOOD REF CE750 M/M 21-51-00.