How to Clean Air Conditioner Coils - ProfessionalSkills
Just like with the evaporator coil, begin by using a soft brush or vacuum to get rid of dirt and debris from the coils, and make sure to clean the base of the condenser unit too.

Cleaning Evaporator Coils - DIY Ideas and Tips
Coils today are usually made of aluminum and don't react well to minerals. Spray on, let it drip to the pan, and then I gently use a soft vacuum brush.

Maintaining Your A/C Condenser Coils - EnergyMonitor
A little more advice: when cleaning coils, be cautious not to bend the fins. Avoid using a pressure washer or anything too powerful.