The best seal around air conditioning lines penetrating siding / wall would be provided by a spray expansion foam. You can get this product in any local hardware (check this site – http://greatstuff.dow.com – this is one of the popular brands). There are high medium and low expansion types (it’s described on the container label).
The high expansion foam might cause some wall / siding deformation. Maybe medium-low would be best for this project. Before you spray the foam into the gap around AC lines remove all the debris and old insulation, slide new pipe insulation onto the thicker AC line, and if possible into the wall (you can also get this foam sleeve insulation in the hardware store in a form of a black or gray soft pipe – solid or sliced along its length for easy installation).
After the expansion foam dries out completely it can be trimmed with a knife and painted to match the wall color.