As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXIING, TURNED LEFT PACK ON AND THE COMPRESSOR DISCHARGE AND SUPPLY TEMPERATURES RISED RAPIDLY, ACCOMPANIED WITH SMOKE IN THE CABIN. RETURNED TO GATE. FOUND LEFT HAND PACK COOLING DOOR CHECK VALVE STUCK OPEN. OPERATIONS CHECK VALVE PER MM 215500.