As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT GATE AFTER TURNING ON RIGHT PACK PASSENGERS REPORTED BURNING SMELL. SIMULTANEOUSLY THE RIGHT "PACK" LIGHT ILLUMINATED. GROUNDED - YES. FOUND RIGHT HAND ACM SEIZED. REMOVED AND REPLACED R/H PACK AIR CYCLE MACHINE, OPS AND LEAK CHECK GOOD. NO MAINT LIGHT OR PACK LIGHTOUT, NO ODOR NOTED IN CABIN REF B737-9 AMM 21-51-04.