I did some research and with some people's help, I think my AC pressure sensor/pressure switch doesn't work properly. When I try to turn on AC I see the light come on but it doesn't give me cold air. I checked and saw that the clutch doesn't get engaged. I recently did ac recharge and when I bypass AC compressor AC works perfectly. I left it on for like 15 min and it was giving me ice cold air. So we know air compressor works just fine. I also checked the relay and put it different fuse it didn't change anything.
I think I will just replace the AC pressure sensor on 2007 Buick LaCrosse. Before that do I need to do anything else? Simply unscrew and screw the one and give it a try?