As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
1.DURING CLIMB +-29000, HEARD A LOUD NOISE LIKE AN EXPLOSION , SELECT ECS AND SAW BOTH OUTFLOW VALVES CLOSED BUT RATE OF CLIMB +-1700. CABIN ALT REACH +- 10000. THE EQUIPMENT COOLING WARNING LIGHT CAME ON. PERFORMED CABIN ALT (QRH) DESCENT TO 10000, BACK TO DEPARTURE.