AC won't cool when car at idle?

The 2005 Equinox had a badly designed connector on the condenser fan. Replacing the fan, and the harness plugging into it, is the easiest but most expensive fix. You might want to try just cutting and rewiring it yourself until next year. The problem was no condenser fan to keep the condenser cooled at red lights -- your refrigerant level was fine.

Adding refrigerant to a system that does not need it is harmful, especially to one with a non-functioning condenser fan. The higher high-side pressure caused when you idle at red lights now will either cause the high side cut-off switch to blow, or the compressor to self-destruct. Either event will be costly, although a blown compressor is much more and also involves replacing a few more components and adding a flush-out step. Have a shop properly evacuate and re-charge the system to avoid problems with the sealed system if the compressor has not yet blown. Maybe they can also rewire the condenser fan for you.

GM's usually have dual speed radiator fans that operate off of 3 relays. If the high speed isn't working, you'll get this problem. Read the post below and scroll down to the wiring diagram to see how the system works.

http://ricksfreeautorepairadvice.com/my-car-overhe...

If you're absolutely sure that the fans are running at high speed when you're at idle, then you've got a different problem. If so, read this post

http://ricksfreeautorepairadvice.com/fix-ac-in-car...

Make sure the engine fan is operating at idle.