My Saturn Ion2 has been having issues with the temp and AC. When I sit at a light my AC is no longer cool and my engine slowly heats up. As soon as I get moving again the AC becomes cool and the engine cools down to normal. Also, when sitting still the engine will occasionally rev but only when the AC is on.
Sound's like your radiator cooling fan is not working when the a/c starts blowing hot see if the radiator fan is working. If it isn't see if you have power and ground to the fan motor if you do you have a bad fan motor. Let me know what you find.