Dash Vents not working

[fowlfixr91]

Hello all- I'm new to this forum as I just purchased a '91 240SX for my son and will be soliciting advice on correcting certain issues. The car itself is actually a pretty good example, a little tired but not too beat as it has sat for the past five years and previously was owned by a little old lady (believe it or not!). No rust, minimal body issues, solid suspension/ steering, strong motor, (auto) trans in good working order, overall a great first car and an excellent platform for future mods (five-speed, hotrodded motor, suspension tweaks, body kit, etc.). Before we get into any major makeover though we first need to fix what's broke, and that would begin with the A/C plumbing under the dash. The upper dash pad itself has a few cracks in it which we will probably 'correct' with one of those plastic covers but worse is that when we attempt to turn on the AC the air only comes out of the defroster vents which seems to indicate that some kind of door mechanism inside the dash is stuck in the 'defrost' position. I'm a reasonably competent mechanic with good facilities and plenty of tools so what I'd like to know now is how do you go about getting the dash apart without breaking anything else so we can get in there and find out why the AC plumbing is stuck in defrost? Also, the system is not blowing cold (a real problem here in SoCal this time of year!!) and as the car is a '91 I was wondering what kind of refrigerant Nissan was using then...I know that was around the time that the changeover from R12 to 134a was occurring. Any and all advice that we could get would be greatly appreciated- I presently own five other cars, all American, but these little 240's have always been among my favorite Japanese cars and I'm really looking forward to making it into something that will look cool, go fast, and be a lot of fun. Thanks all...