What was found
ACFT RETURNED TO PLATFORM DUE TO AFTER ENGINES START, THE "TAIL COMP TEMP HI" LIGHT TURNED ON. MX REPLACED THE THERMO SWITCHES ON BOTH SIDES IAW MM 36-20-02 AND THE ACFT WAS DISPATCHED. AFTER THAT, THE ACFT RETURNED TO DEPARTURE, DURING CLIMB AT 9,000 FEET, THE "TAIL COMP TEMP HI" LIGHT TURNED ON AGAIN. MX DETECTED A RT AIR CONDITIONED DUCT BROKEN, SO THE DUCT WAS REPLACED IAW MM 36-00-00, TESTED CORRECT.