Upon arrival, firefighters discovered light smoke at the ceiling level inside the store and a heat source coming from the ventilation system on the roof. The smoke was coming from a rooftop air-handling unit, the motor of which had froze, causing it to overheat and burn up, Dickerson said. The fire was out, and then power was shut off to that unit. The store’s manager was told to contact company maintenance personnel to fix the problem. Firefighters ventilated the store and then returned to the station at 2:30 p.m.