What was found
WHILE TAXIING TO 36R THE FA REPORT TO THE CAPTAIN ABOUT SMOKE IN THE CABIN. THE CAPTAIN AND FO STARTED SMELLING BURNT RUBBER IN THE COCKPIT. PILOT TURNED OFF THE PACK AND DECIDED TO RETURN TO GATE. THE SMOKE CLEARED BY THE TIME THEY GOT BACK TO THE GATE. INTERROGATED MDC AND FOUND N1 CODE 211943. T/S IAW CRJ 900 FIM 21-61-00-810-817 A01. RFR TEMP CONTROL VALVE 2 "MPE14", IAW CRJ 900 AMM 21-51-20-0/400-801. PACK 2 OVERTEMPS AND AUTOFAILS DURING OPERATIONS TEST. R & R NR 2 PACK DISCHARGE TEMPERATURE SENSOR, IAW CRJ 900 AMM 21-51-22-000/400-801. OPERATIONS CHECK BAD. PACK STILL AUTOFAILS. CONTINUED TBS OF RT PACK. FOUND LITTLE TO NO EXHAUST FLOW. REMOVED RT ACM, IAW CRJ 900 AMM 21-51-08-000-801-A01. NEW ACM TO BE INSTALLED.