Little information on the energy efficiency of MAC systems is published. MACs are custom-made for car manufacturers and installed during the production of cars, but their COP is usually not publicly known. The additional fuel consumption of a MAC depends on many factors such as ambient temperatures, humidity, rotation speed of the motor, car model and refrigerant type. Estimations range from between 3 and 18% in the EU or the US to around 20% in China and India. COPs found in various scientific papers range from 1.6 to 4.0, but this does not mean that commercially available systems actually have COPs in this range. Competition between various refrigerant MAC systems has led to improvement in all systems over time.