Must my new air conditioning unit be 3 feet from the wall (or positioned backward)?
According to Trane installation instructions, the technician is correct. They do require 3' of clear space in front of the control box.


  




As for why the technician chose this orientation, I can only speculate. It looks to me like the access panel is on the corner of the unit, which would mean there has to be 3' clear space at the corner. Obviously the technician could not install the unit in these two orientations.



Since then the building would encroach upon the clear space required. This only left him with two choices.

  

Given these two choices, I would agree that the technician made the best choice.  If the unit would have been installed in the other orientation, it would have potentially left the line sets in the path of folks moving through the gated area at the corner of the building. 

In the end. If you're not happy with the installation, you should contact the company and discuss with them what options are available.