Freeon

That vehicle came with R12 from the factory so the system has to be retrofit to accept R134A. There are a number of things that has to be done to it first so I suggest you find a reputable shop to assist with that.

I ran a quick search here, these posts might interest you!

https://www.2carpros.com/questions/dodge-spirit-1991-dodge-spirit-need-to-retro-fit-to-r134a

https://www.2carpros.com/questions/1993-ford-aerostar-flushing-an-uncharged-ac-system-that-has-satup-sence-05

More info might be found, by revising the search

Found this also

http://www.youtube.com/results?search_query=how+to+retrofit+to+R-134+refrigerant&aq=f

Am I Good or What!!!!

The Medic