I've recharged my A/C system and troubleshooted it a couple of times.
Double check all of the fittings first. No point in buying Dye to fill your system if the problem is rather simple. This sounds like a dumb idea especially if you've fixed your A/C system before, but it happened to me. I replaced all of the seals, the valves, the canister, the orifice tube, and refilled the system. 1 year later (two days ago), I wanted to use the A/C for the first time and it wouldn't come on. The whole system was empty with a pressure of 0. I filled it up and I instantly heard the hissing sound of the leak, which happened to be the fitting right next to the valve. It was so loose you could turn it by hand, and I know I tightened it the first time I did this job.
If that doesn't work, buy the UV dye and use that in the system first. The dye can is pressurized, and if the leak is that large, you should be able to locate it instantly. As mentioned, the color is unmistakable. Mine is a very bright neon green.
If you find that there'* a leak somewhere at a fitting that'* already tight, you'll want to pick up an o-ring kit to replace all of the seals. While you're at it, replace the orifice tube, which is around $1 and gets clogged often, and replace the high and low side valves. Those are fairly cheap to replace.
Not sure how Bonnevilles are as I only did this job on my Regal, but you should be able to use just two conventional cans of straight refrigerant (not the larger and taller refill cans). You'll want your pressure to be between 30 and 40 psi while the A/C is running.
2005 Pontiac Bonneville GXP - For Sale ----- 1995 Buick Regal GS(X) - L67 madness
2000 Buick Regal GSE - Stock...for now
----- 1987 Jaguar XJ-* V12 - 12>8