DAF's EURO-6 air-conditioning (A/C) system operates with hysteresis on/off control. Current selected controller values are the same for every weather condition. Air conditions are the combination of temperature and relative-humidity. In this paper we present fuel saving based on improved controller values.We expect a potential fuel saving from 0.1 upto 0.5 percent of the total truck fuel consumption without load, depending on the ambient weather condition. For research this requires the development of an A/C model. A two-state heat-exchange graybox model is identified using measured data, containing inlet air and compressor speed as input and compressor torque and outlet air as output. Model is characterized using cross-validation with a validation data set and compared with existing models. A method to determine the cabin inlet relative-humidity given comfortable climate temperature of 20[oC] is provided.