Air Conditioner See Also: Heat Pump, Refrigeration Mechanical process for controlling the Temperature, humidity, cleanliness, and circulation of Air in buildings and rooms. Most air conditioners operate by ducting air across the colder, heat-absorbing side of a Refrigeration apparatus, and directing the cooled air back into the air-conditioned space. Small window conditioners vent Heat outdoors. Larger systems use circulating Water to remove heat. Air conditioning provides the heat, humidity, and contamination controls essential in the manufacture of such products as chemicals and pharmaceuticals. Air conditioning Motors are classified as prone to stall motors because they are designed to work against high vapor (see States Of Matter) Pressure. The easier an air conditioning motor stalls, the harder it is to restart after a fault (see Fault Current). Studies show (IEEE paper, Stalled Air Conditioner Compressors, Transactions on Power Systems, August 1992) that prone to stall motors can stall on faults lasting over five cycles and nominal Voltage levels less than 60 percent.