What was found
(CAN) THE FLIGHT CREW EXPERIENCED A BLEED HOT CAUTION LIGHT ACCOMPANIED WITH TORQUE FLUCTUATIONS ON BOTH ENGINES. THE AIRCRAFT RETURNED TO THE POINT OF DEPARTURE. MAINTENANCE INVESTIGATION REVEALED THAT THE BLEED DUCT TO THE AIR CONDITIONING BAY HAD SEPARATED AT THE AFT END OF THE SPINE WHERE IT ENTERS THE AIR CONDITIONING BAY. THE INCREASED VOLUME OF UNRESTRICTED BLEED AIR TRIPPED THE DUCT OVERHEAT SWITCHES, AND CAUSED TORQUE FLUCTUATIONS DUE TO SWITCHING BACK AND FORTH BETWEEN LOW AND HIGH BLEED. THE DAMAGED DUCT AND PERISEALS WERE REPLACED AND THE AIRCRAFT RETURNED TO SERVICE.