What was found
FLT 433, BOS-MCO, AIR RETURN TO BOS, COCKPIT AND CABIN TEMP UNCONTROLLABLE, FULL COLD SET AND AIR TEMP 156/COCKPIT TEMP GREATER THAN 100 FWD TEMP GREATER 90 IN DESCENT BACK TO BOS, TEMP WENT FROM 156 TO 110 WHEN A/C IN IDLE FOR A WHILE INCREASED BACK UP WITH PWR UP. REMOVED AND REPLACED ZONE TEMP CONTROLLER & NR 1 PACK TEMP CONTROLLER IAW 21-63-34-04 & 21-61-34-04-01, GND CHECK OK. ACCOMPLISHED CONFIDENCE FLIGHT, ISOLATED TEMP RUNAWAY TO LEFT PACK, REMOVED AND REPLACED PRIMARY HEAT EXCHANGER UNIT, OPS CHECK OK.