I've read some comments about how to access the Trane XL1800 condensing unit to clean the fins. None has clearly stated how to remove the top in order to remove the side panels. The side panels have a screw at the top which is shielded by the plastic top grilles. I don't see how to remove the plastic grilles without damaging them.

You don't need to remove the side panels at all. Just turn the power off. Remove the top and hose it down with water inside than outside. Wait a bit, close it back up, wait a bit lonbger and than turn power on.