As my buddy walked up the driveway, he noticed my condenser (the exterior unit of my central AC system), which was caked with dirt, grass and even a few dead insects. He gave me a look that said, "You're an idiot." Then he gave me a sermon that only a heating/cooling engineer like himself could deliver. I didn't understand most of it, but I got the key point: When the fins surrounding the unit are dirty, the fan can't efficiently suck air through them and the whole system has to work harder to cool the house. That costs money in the form of higher electricity bills and future repairs. Since then, I've cleaned my condenser every spring. It's so easy that a kid can do it in about 20 minutes.
Cut off the power so the fan can't cut off your fingers. Your power box may have a switch inside or a block that you pull out to cut the power.
Vacuum the fins with a brush attachment. Be gentle so you don't bend the fins; they aren't much tougher than tin foil.
Unscrew the fan grille, set the fan aside and rinse off the fins. Dial down the water pressure so you don't damage the fins. Put it all back together and pour yourself a cold one.
— Gary Wentz, Senior Editor
Springtime central air maintenance
How to cover up your AC unit in the fall
How to clean a window air conditioner