As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNABLE TO CONTROL CABIN TEMP, SUPPLY DUCT TEMP WOULD NOT GO BELOW 88 DEG F. F/A REPORTS THAT AFT CABIN IS VERY HOT, MID A BIT COOLER. FOUND THAT AN INCREASE IN POWER WOULD CAUSE A MOMENTARY COOLING. ONCE NORMAL CRUISE POWER WAS ESTABLISHED. TEMP WOULD GO BACK UP AND COULD NOT BE COOLED. SUSPECT A POSSIBLE BLEED AIR LEAK. AC WAS DIVERTED BACK TO DEPARTURE AIRPORT.