The first step is to turn off the power, obviously, then remove the grill and clean it. Unscrew the top grill and hold it open. The fan will usually come with it, so support it carefully to avoid stretching the electrical wires and stressing the connections. If the fan doesn’t lift out, avoid hitting it with a direct spray of water when you clean the fins.
Vacuum the condenser fins with a soft-bristle brush attachment. The metal fins are very delicate, so take special care and avoid bending them. Clear away weeds, grass and other debris that block airflow through the coil. You often have to unscrew a protective metal case and lift it off to get at the condenser fins.
The fan inside the condenser coil brings in air through the fins, and that air contains dirt and debris such as dead grass, leaves, dust and more. Any of this debris that collects on the units fins will reduce airflow and hurt the air conditioners efficiency. In particular, grass clippings and spores from cottonwood trees and dandelions can really affect your AC system. During spring, you might need to clean the fins on a weekly or even daily basis.
This would also be a good time to make sure your fan motor is properly lubricated, if you can get to it. If you see lubrication ports, get some special oil that is used for electric motors (do NOT use penetrating or all-purpose oil) and apply five drops of that oil to the ports. There are several AC models with fan motors that do not have oil ports and therefore cannot be lubricated. Make sure you check your owners manual if you are not sure.
Typically, the compressor and motor are sealed and wont require maintenance. But if you have an older compressor that is belt-driven by a separate motor, you can lubricate that motor through its oil ports. Make sure you watch for dark drip marks on the bottom of the compressor case, because this could indicate an oil leak. In addition, the compressor or tubes could be leaking coolant. If you find this leak, please call a professional NEVER try and tighten the joints or you could make the problem worse. Plus, only a professional with the right equipment can recharge your system with the correct level of coolant.