Enclosure air conditioners remove the heat generated by electronic devices from the inside of cabinets or enclosures. They typically use refrigerants and include thermostatic controls to maintain programmed environmental conditions. Some devices automatically evaporate condensate, eliminating the need for draining. Others include an air flow sensor that monitors the temperature of the condenser and ensures that blockage or contamination does not compromise cooling efficiency. Enclosure air conditioners use either single-phase or three-phase power and vary in terms of cooling efficiency, which is often expressed in kilowatts, tons of refrigeration, or British thermal units (BTU) per hour. Devices that use direct current (DC) voltages operate at 12 or 24 VDC. Devices that use alternating current (AC) voltages operate at 115, 230, 380/400 or 460 VAC. For AC devices, frequencies include 50, 60, and 400 Hz. Typically, 400 Hz devices are used in aerospace applications.