At 0925 hours Squad 58 was alerted to a possible building fire at the Limerick Diner after staff and patrons smelled and seen a haze. CH58 arrived and was assigned to the roof. SD58 arrived and was assigned to check the basement. EN58 arrived and stoodby in the manpower pool. A HVAC unit on the roof with a bad belt was the cause. Units were in service for approximately 30 minutes.