What was found
(ETOPS) FLT # 20, LHR-JFK. TEMPERATURE IS DROPPING TO 60 IN ALL ZONES WHEN PACK IS ON LOW OR MEDIUM . INCREASES TO SELECTED TEMPERATURE ON HIGH; PERFORMED OPS TEST OF COCKPIT + CABIN TEMP CONTROL WITH CFDS/MCDU IAW AMM 21-63-00-710-004-A TEST PASSED. NO FAULTS NOTED. ABLE TO CONTROL CABIN TEMP WITH NO ISSUES. NO FAULTS REPORTED BY THE MCDU IN THE LAST LEG + PREVIOUS LEG REPORTS. NO CLASS 3 FAULTS. PER TSM 21-63-00-810-822-A PERFORMED OPS CHECK OF TEMP CTRL WITH MCDU PER AMM 21-60-00-710-004. NO FAULTS FOUND. ALL OPERATION + INDICATIONS NORMAL. ABLE TO CONTROL + VERIFY TEMPERATURES. TEMP CTL TEST PASSED. LAST LEG + PREVIOUS LEG REPORTS INDICATE NO FAULT. ALL INDICATED PRESSURES + TEMPS NORMAL (SUPPLEMENTAL FOR ADDITIONAL INFORMATION AND TO PROBLEM DESCRIPTION)