Yes much like the indoor coils that are protected from dust in the air, the outside unit does not have this protection. The biggest killer of AC systems is plugged coils. It not only raises pressure it raises your utility bills.
Take a garden sprayer, and spray up and under the fins. Do not use the real hard direct spray pattern, as the pressure could bend the fins over. Simply rinse it off in that manner. Take care not to spray right in the area of the electrical power entrance just for safety. I would also suggest not to do this when running, or you will get a face full of water when the fan is running.
If your unit is near your discharge from the dryer vent, check carefully for lint deposits. If this is heavy build up, your better off having the unit professionally cleaned as it will require some dismantling of the unit to remove the lint.