It's commonly believed that if you cover your air conditioner, the unit will function better because it's not in the direct path of the sun and—thus—won't have to struggle against its hot rays to cool your home. While there is some truth to this piece of advice, it's not as simple as you would think. Here's the whole story about shading your air conditioner to ensure you do it correctly.
The Surrounding Temperature is More Important
The thought behind shading an air conditioner is that the sun's rays causes the unit to heat up, so the unit must expend extra energy cooling itself while also conditioning the air. However, the energy savings obtained by decreasing the heat gain caused by direct sunlight are minimal, because the sun's rays aren't reason the unit is working so hard. It's the ambient temperature surrounding the air conditioner.
The air conditioner pulls in air from the outside, cools it, and sends the result to your home's interior. The hotter the air is from the source, the more work the A/C unit must do to reduce it to the desired temperature. This is one reason why your energy bills are typically lower in spring and fall when outside temperatures are cooler and higher in the summer when the temperatures tend to be hotter.
Using Shade to Your Advantage
Unfortunately, when shading an air conditioner, people tend to only cover the unit itself. As noted previously, this doesn't help much, because only the small sliver of air space around the unit would be a lower temperature than the rest of the ambient air. Air conditioners take in thousands of cubic feet of air per minute. So to have any impact, you would actually need to cover a larger area.
This is why many professionals recommend people place their air conditioners on the north side of their homes that typically doesn't get a lot of direct sunlight or where there are a lot of trees shading large swathes of area. The air tends to be cooler in these places, which will reduce the load on your air conditioner unit.
Shading Still Helps
Covering your air conditioner still helps, but in a different way. It can protect your unit from damaging ultraviolet light present in the sun's rays, which tends to break down plastics fairly quickly. Since air conditioners are made using plastic, shading you A/C may slow the degradation and extend the unit's lifespan.
It's important you avoid blocking any of the unit's vents, though. Blocking the ports where air is drawn in and/or discharged can make it harder for the unit to properly cool your home or even result in premature breakdowns.
For more information about this issue, contact an home air conditioner repair service in your area.