1. INADEQUATE MAKE UP AIR. Apart from a broken fan belt, problems with the make up air is probably the 2nd biggest cause of hot kitchens. Things to check include: The belt on the make up air is broken, the make up air filters need changed, or there is inadequate make up air. There are simple ways to test if makeup air is inadequate. If there is a rush of air into the restaurant each time the door is opened it means more air is being sucked out that is being brought back into the building. This means the kitchen exhaust fan is creating negative pressure in the building. In some instances, only a company that specializes in testing and balancing commercial kitchens can resolve the problem. If you are exhausting 400 cfm of air you must be bringing in 400 cfm or you will be exhausting your heated air or air conditioning. 2. MOTORS RUNNING BACKWARDS. This typically happens with new grease exhaust fans or when a motor has been recently changed. Two hundred twenty volt (220v) motors operate clockwise and counter-clockwise. If the two hot wires are switched the motor will reverse directions. On a grease exhaust fan it will still seem like the fan is blowing air but this is just actually from back pressure and the fan is not properly exhausting air. Generally this is characterized by very weak suction at the hood. 3. Each piece of cooking equipment has varying hot air exhaust plumes. The hot air plume of a fryer increases significantly when frozen foods are added. The plume of a grill increase when fresh hamburger is added but less significantly than the fryer. Be sure you cooking equipment with the greatest plume is placed in the center of the hood or directly under ducts. Also, be sure that the equipment sits at least 4 inches from the front edge of the hood. 4. Be sure the air passage between the filters is clear of grease. See picture 7 above. Improper or infrequent grease filter cleaning may lead to baked on grease and carbon deposits in this area. Hot air must be able to pass through the grease baffle filters. These deposits can be impossible to clean. Built up grease between the grease filter baffles can severely restrict the airflow through these grease filters. This restriction can severely impede the grease and hot air exhaust capabilities of the grease exhaust system. 5. Be sure the pulley is not slipping on the shaft. Check that allan head set screw is tight and that square key bar is in place. See picture 8 above.