What was found
SMOKE ENTERED THE CABIN DURING TAXI OUT. THE AIRCRAFT WAS RETURNED TO THE GATE. THE AIR COND TURBINE NOZZLE C/B POPPED WHEN COLDER POSITION SELECTED. MAINTENANCE FOUND WIRING CHAFING/SHORTING TO RT TURBINE NOZZLE SHUTOFF VALVE. THE WIRING WAS SPLICED AND THE WIRE BUNDLE WAS REPOSITIONED. THE AIR CONDITIONING SYSTEM OPERATED NORMALLY. SMOKE APPEARED IN THE CABIN AGAIN DURING TAXI IN AT EWR. THE RIGHT PACK WAS TURNED OFF AND THE SMOKE CLEARED. MAINTENANCE FOUND THE RT AIR CYCLE MACHINE AT FAULT. THE RT ACM WAS REMOVED AND REPLACED, OPERATIONAL CHECKS WERE GOOD WITH NO SMOKE DETECTED.