What was found
MFR FLIGHT NR 2420: PAX REPORTED BURNING RUBBER ODOR AT SEAT 1AB. TURNED OFF NR 1 ACM AND ODOR WENT AWAY. MAINTENANCE PERFORMED EXTENSIVE GROUND RUN OF A/C OPERATING ACM'S TOGETHER AND INDIVIDUALLY SELECTED VARIED TEMPERATURE SETTINGS DURING OPS CHECK. NO FUMES NOTED AT ANY TIME. UTILIZED INPUT INSTRUCTIONS OF SERVICE LETTER DH8-400-SL-21-012A AS A PRECAUTIONARY MEASURE, AGAIN NO FUMES NOTED. NO PARTS REPLACED. AIRCRAFT WAS RETURNED TO SERVICE.