As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LEFT PACK OFF AND L ENG BLEED OFF AFTER PUSHBACK AND AFTER START CHECKLIST. L DUCT PRESSURE DROPPED TO ZERO. R DUCT PRESSURE NORMAL AC RETURNED TO THE GATE (BTB) MTX GROUNDED A/C ,MTX PERFORMED LH ENGINE RUN REF AMM 71-00-00, NO FAULTS NOTED AT THIS TIME RETURNED A/C TO SERVICE. .