In T47140#484595, @stephen paschke (paskperfect) wrote:

Confirming that under MacOS 10.13.3, Blender Vers 2.79a hash 61335d8 is working as advertised:

1. Stereo (2-channel) wave file does not pan.
2. When Mono button is clicked in the strip's properties, wave file will pan from left (-1) to right (+1) on monitoring output.
3. panning from -1 to -2 and from +1 to +2 re-centers pan in 2-channel output, when Mono button is checked.

*Edit*
Never mind, its working :3
You have to literally Enter "-1" or "+1" for hard panning.
Also, If you slide slow you will notice the subtle change.