The AC blows perfectly cold while in motion, and after being stopped for a bit. eventually, the air coming from the vents becomes much warmer. upon driving again, the temp goes back to cold. need assistance please. also, when its not very cold, we get what seems to me a burning coolant smell in the vehicle. if we let it stay on too long, the smell is almost overwhelming. anyone know why this is occurring. (i'm no mechanic, just trying to save some $$$$!)