The good news? Its R-134A...and you can purchase it yourself. The bad news? If your refrigerant is gone, you must repair the leak. -And if your system is completely empty, that means the system has drawn in moisture from the ambient atmosphere. Its likely the receiver/drier is soaked. If you simply shoot refrigerant in and run it, that means your system would circulate contamination.... that is basically cancer to your system.
First, rent a refrigerant leak detector(its a hand held halogen sniffer), give the system a small charge, and run the detector over all the connections, (including the high and low side ports/schrader valves), the back of the compressor, the space where the evaporator sits, and anywhere the lines go from rubber to metal.
When you find the leak, take it apart at that connection, take the o-ring to Oreilley's (autozone sux), make sure and tell them its for a/c. Get a new receiver-drier (it may come with new o-rings),get a new orifice tube and a tool to remove/install it....remove the old one. get a can of a/c flush and flush the evaporator and the condenser, get about 3 lbs refrigerant, and at least 6 oz of esther oil. blow the system dry with compressed air..put in the new orifice tube. At this point, don't take the caps off the new receiver until you are ready to install it... and don't dilly-dally: leaving the new receiver open to the ambient air will ruin it. Get it all put back together, and then rent a vacuum pump. Evacuate the system for at least 6 hours, or until you get down below 30 inches of vacuum.(preferably to around 150 microns). Call your Pontiac dealer and ask the service dept for the correct charge, or it may have it printed on a sticker somewhere around the other info stickers (catalyst etc..).
Now, without the engine running, put on some a/c gages, put on a refrigerant container, bleed the lines, and don't allow any atmospheric air to enter the system. Shoot the esther oil and about 1.25 lbs into the system through the low side. Start the engine and set the a/c to max cool. Roll down the windows. let the system circulate about 5 minutes, feed the rest of the charge in the LOW(blue) side(gas if possible, not liquid). Do not even open the high side... and DO NOT UNDER ANY CIRCUMSTANCES allow any liquid refrigerant to enter the compressor as that will result in catastrophic failure. Confirm by calculation you have the correct charge, leak test the system again, confirm no leaks -you can tighten any connections that may trip the leak detector, but don't over-tighten them.
System charged......enjoy your summer
