You need to build a screen system that allows any water that hasn't evaporated to filter through. Think of it like a shield system. I would build it at least 6-12" away from the coils and cap off the top. This would force the incoming cooler air through the screen. Any build up would be on the screen material instead of the coils. I would suggest the poly window screen material to build with.
I built a sun shade that kept the condenser coils out of the sun fer my friend in San Antonio as his AC was working hard and hardly cooling. His condenser unit got full sun all day until the evening time (about 5pm). Needless to say, the umbrella like shade made it much cooler in his house that you almost had to use blankets in the main room. Total cost fer the big roll of shade was about $30...6' wide by 20' long. I only used about $15 worth fer the condenser unit. It's that sun shade stuff you put over yer patio...usually in green, black, or ivory. You can even buy it in bulk, too! I even put some on some of the windows that were facing the sun. Key point is to keep the heat out of the house in the first place, right? That kept that bedroom temp stable as it would always feel like a furnace when you went in there.
What do you think?