This is a house in Noble Oklahoma that shows spalling of the brick siding. 

Spalling is the surface cracking of brick or concrete and is an indication of a moisture problem.

With this particular house the freon line for the AC compressor has no insulation after it enters the wall.  When the AC is ran in the summer time, the pipe condenses any moisture in the air and that moisture runs down the pipe and into the brick.  The brick soaks up the moisture and with a combination of time and freezing temperatures causes what you see here.