Recharging my A/C

Hey everyone, I just had a quick question. I have a 2002 G20, and I was trying to recharge the air conditioning the other day. I hooked up to the low side line, turned on the car and the a/c, and started charging. I used about half the can, and the gauge told me I was overfull.

Got in the car, not real measurable difference. I never heard the fan clutch kick in; and by the next day, the temperature felt like I hadn't done a thing to it.

I have the ATC panel, as I'm sure everyone else does as well. Is there some way to force the compressor to come on, like I can do in my Jeep?