A method for operating a climate-control system of a vehicle using an initial ambient (outside the vehicle) air temperature calculated based upon a current air temperature measured by a temperature sensor located on a side-mirror of the vehicle. A previous air temperature is stored at or before an engine shut-down time. At a subsequent engine start time: a) the temperature sensor on the side-mirror determines the current air temperature; b) a solar radiation on the vehicle is measured; and c) a duration since the previous air temperature was stored is determined. If, at the engine re-start time; a) the duration exceeds a threshold value; and b) the current air temperature is higher than the previous air temperature, then the initial air temperature is calculated from: a) the current air temperature, b) the previous air temperature, and c) the solar radiation. The climate-control system is operated using the calculated initial temp.