What was found
AFTER 40 MINUTES OUT OF HNL FLIGHT 2039, AIRCRAFT LOST PRESSURIZATION, COULD ONLY MAINTAIN 10,000 FT, CARGO COMPARTMENT OVERHEAT LIGHT CAME ON SHORTLY AFTER. ACCOMPLISHED AIR TURN BACK TO HNL. REMOVED AND REPLACED CARGO COMPARTMENT AIRCONDITIONING HEAT EXCHANGER AND ACCOMPLISHED ENGINE RUN UP, USING BLEED AIR SYSTEM, OPS CHECKED GOOD PER MM CH 21.