Shortly before 0600 this morning, Station 21 was dispatched for a commercial fire alarm activation at a hotel in the district. E21-2 arrived on scene within minutes and discovered a heavy smoke condition and a working fire in an unoccupied room on Division 2. Crews got a quick knock with a water can and a 400' line and were able to isolate the fire to a malfunctioned HVAC unit with no extension or reported injuries. Outstanding work to all agencies and crews involved!