Below is a list of Central Air Conditioners manufacturers from Frederick, Maryland. Central air conditioners remove heat from the air of an entire building through the use of a compressor, a condenser, an expansion valve, a thermostat and motorized fans. Central air conditioning units are connected to air ducts that deliver cool air throughout the house, office, school or other structure. The popular belief about air conditioning is that it introduces cold air into a warm area when in reality it removes heat from the air, which makes it feel cooler. This is similar to evaporative cooling.