Hissing Sound When AC On

If anyone could help me out with this or at least point out what the problem might be, I would really appreciate it.
When I turn the AC on, I start hearing a hissing/sucking type of sound from under the dash. The air is not cold....but I touched the pipe coming into the cab (a little above the gas pedal and it was COLD). It hisses even if I switch to heat (swirl the knob to the red side) and only stops when I press the AC button.

This is on a 2006 Nissan Quest.

I can make a video of this if it would be helpful (anyone actually willing to help)

There are a few TSBs for the 2006 Quest and the A/C. Here are two attached to this reply.

There are a few TSBs for the 2006 Quest and the A/C. Here are two attached to this reply.
Thanks for the reply, I will go through those and maybe find something.
Do you have any idea what I should be looking for, though?