What was found
(CAN) THE CREW MADE A GATE RETURN AS CABIN TEMP COULD NOT BE CONTROLLED IN MANUAL OR AUTO MODE. AFTER A SYSTEM RESET AND ENGINE START THEY BEGAN TO LEAVE THE APRON WHEN THEY HEARD A CLUNKING SOUND FOLLOWED BY VISIBLE SMOKE IN THE FLIGHT DECK AND CABIN. THEY RETURNED TO THE GATE AND PERFORMED A RAPID DEPLANEMENT. MAINTENANCE FOUND THE ACM (AIR CYCLE MACHINE) SEIZED. P/N: 782790-18 S/N: 910242 TSN HOURS: 53708 , CYCLES: 65868 TSR HOURS: 270 , CYCLES: 339 A/C HOURS: 64432 A/C CYCLES: 66039 (TC# 20190726022)