There is a good chance that you have a leak which must be taken care of but if you just want to A/C to last for a short while try this thread.

http://www.contour.org/ubbthreads/showflat.php?Cat=&Board=zetecmaint&Number=1266077&page=1&view=collapsed&sb=5&o=31&fpart=1

"Always do the cheap and easy ones first." 1996 V6 ATX 96K miles