Here's a good study on A/C shading. Shading's not as helpful as common sense would make you think..Note the surprising volume of air a system moves through the condenser. No wonder shading can be problematic in regards to minimizing re-ingestion of hot air by the unit.

http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-302-96/index.htm

Misters on the condenser can help but not many areas have good enough water quality not to cause damage over the long term from scale buildup or corrosion. Here in cent FL, there is a premium condenser spec that is used for beachside installs...special coils made to withstand salt air corrosion. Also hear some AC pros warn about compressor damage from liquid entering compressor because the coils were over-cooled during certain ambient temperatures but this may be anecdotal.

If you are in a hotter area like Florida or Texas, consider a heat recovery unit for free hot water and further A/C efficiency increase. A $30-$50 monthly saving is average.

http://www.trevormartin.com/about.asp

http://www.p2pays.org/ref/11/10104.pdf

http://www.turbotecproducts.com/EPhome.html

The last link has a neat savings calculator. These units have been around for decades and kick solar hot water to the curb every time in hotter climates.

The upside to a mister on your condenser coil is they do work.

The downside is the consistent moisture exposure causes a standard cabinet to rust and rot expeditiously. I have seen 3-4 year old units look like they are 20.

In addition besides the misters plugging easily by hard water if not softened, the condenser coils themselves become coated with calcium, lime, TDS or raised salt levels from a softener coat and eventually reduce airflow and temp exchange. When a coil is kept damp, the small airborne particles also instead of passing through will stick to the damp surface and set up like a paste, which is difficult to get off and furthermore reduces the efficiencies in time.

They do work though and can squeeze a bit more capacity out of the unit. You may wish to consider adding a close on rise stat outside in series with your electric circuit to the valve and only use this help on the hottest of times, like 95+.

Direct sun on the condensor has a tad of an effect as I once checked myself with a data logger, reading the temps over a period of time but not even close of an effect of a good cleaning or keeping the coil clean.

Mini pergola? You could set a few plants on top and that would look nice through the window.

Like Zl700 said be careful with those misters. They can do more damage than good to the coil and cabinet.

i thought about a mister system, we don't have hard water/lime/calcium buildup issues here. as a matter of a fact i have never even talked to anyone local who has a water softener installed! just not quite sure since i have a 10 year parts and labor warranty and if the misters caused a problem it would likely void it.

whatever i do do i want to keep it far away from teh unit, yet still provide shade. i did sort of think about a pergola or something, just not sure how exactly i would do it.

i wash the coils every couple months or so. we get a lot of dust around here during the summer and you have to wash them out periodically.

I'd be wary of the pergola idea because of how likely it would interfere with airflow.

As Z pointed out, shading is a minimal help. Just because something is hot because it's been in the sun doesn't mean it's possessing a large quantity of heat, it's just at a high temperature. Think of a garden hose full of water as an analogy. When you first turn it on, the water comes out hot and you tend to think 'what a great way to heat water' but after about 20 seconds, the water begins to flow cold with very little temp difference from where it enters the hose to the exit nozzle. The same amount of solar energy is still hitting the hose but the moving water is carrying it away so fast it makes little difference in the water's temp...hence Z needing a data logger to measure any effect of shading on a condenser. Whatever solar energy is striking the condenser cabinet, the fan is blowing away the generated heat much faster than it can make much difference. I see a lot of anecdotal numbers like '10% savings' thrown around but don't think that number would stand up to much critical review. Look how big solar panels must be (and be oriented to present most of their surface area to the sun) to heat anything and compare that to the fairly small surface of a condenser that's exposed to direct sun.
Gary

I suppose there was a little more cooling effect when that big tree was there, not just shading the unit, but cooling the surrounding air which was then passing through the condenser coils.