Good cooling is achieved only in higher rpms. While in city and under 2000 rpms the cooling is slow. When you take the car out of parking, the inside temp is already low. The sension inside the cooling coil gets cooled quickly and sends the signal to the compressor to cut off. When in sun and the air flowing over the coil and sensor the threshold value of the sensor is not met quickly and the cut off occurs late. This also depends on blower speed. On low blower speed cut off occurs quicker than that on high blower speeds.