As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT THE GATE APU ON, RIGHT AFTER TURNED THE LEFT PACK ON TEMP STARTED RISING, COULD NOT CONTROL WITH AUTO OR MANUAL MODE. BURNING SMELL WITH POSSIBLY LIGHT SMOKE AND SMOKE WENT AWAY AFTER LEFT PACK OFF. FOUND LT PACK TO BE UNCONTROLLABLE IN AUTO AND MAN. ALSO THE CAUSE OF SMELL IN AIRCRAFT. DEFERRED LT PACK IAW MEL # 21-51-11.