parts.ramseyinfiniti.com
RE the AC... Agree with whats been posted need to check it out.
Listen to @
mk378
Need to understand how it works... it is not really apparent here but the pulley where the belt rides has a bearing that goes on the compressor shaft. 27633 is the pulley in the diagram. What you see illustrated as a triangle with three flanges attached to a ring is the compressor drive, there will be three large rivets. When the compressor is engaged an electromagnetic coil in the pulley pulls the ring down against the pulley (the flanges are actually flat springs) locking the pulley and drive together and driving the compressor.
WITHOUT the engine running you should be able to turn the pulley (where the belt rides) with reasonable ease and it should not make noise or feel abnormally rough or like it has grit or gravel in it. If that is fine then move onto trying to turn the ring/triangle rivets assembly it should also turn though probably not as easy. Both should turn 360+ degrees, if they will not something is wrong.
If it passes those points then look for any excessive rust or whitish coloring to the pulley/drive hub.
If its good so far then you can get onto the electrics it shouldn't be required to have the engine running to verify engagement of the clutch, setting the system to max defrost and turning the key on should do it for at least momentarily, unless theres something weird with Nissans.
Assuming the belt does not drive something else, I'd likely move this down the list a bit, but as you have time before it can be registered and driven no harm in checking it out.
Speaking of which, I do hope you have a negotiable title on this thing before you spend anymore money.