You can set the direction of a boundary condition.

To set the direction of a load to a known value:

pressure.Direction = Vector3D(1,0,0)

To set the direction of a load using the direction from a face or edge or between points:

sels = ExtAPI.SelectionManager.CurrentSelection
reversed = True
vec = Ansys.Mechanical.Selection.SelectionHelper.CreateVector3D(sels, reversed)  
acceleration.Direction = vec