The temperature approach is the difference between the process outlet temperature and the inlet air temperature. So the approach temperature is probably the process outlet temperature.
The appoach temperature is how close you can get the process side (hot outlet) to the air side (cold inlet). So, if it is ambient 25oC, unless you have a very large oversurface, you are not going to get 25oC in the process outlet, you are going to get it cooled to, let's say, 30 oC, which is a 5 degree approach.