The Fire Department was dispatched to the Eldorado Diner 55 West Main St on a report of smoke and small fire in the office. The first arriving units found an odor of an electrical fire in the office. Engine 237 investigated the odor found one of the air conditioning thermostats had burned out. The crew disabled theromstat.Ladder 55 laddered the roof to check the air conditioner unit in question and shutdown the circuit breaker to the air conditioning unit involved.There was negative extension in the office and the smoke was contained to that area. All units returned to quarters shortly thereafter.