Air Conditioner Maintenance: Why I Hose Off My AC Unit

Quick answer: hosing off the outdoor unit once a year in the spring is enough for most homes. Give it a second rinse in mid-summer if it sits near cottonwood trees, gets hit with grass clippings from the mower, or lives in a dusty spot. If you can see fuzz, leaves or dirt matted on the fins, it’s time.

Why I hose it off

I hose mine off every spring before we start running the air. The outdoor unit (the condenser) works by pulling the heat out of your house and blowing it off through those thin metal fins around the sides. When the fins get caked with dirt, pollen, cottonwood fluff and grass, air can’t move through them well and the heat has nowhere to go. The system runs longer to do the same job, which means a higher electric bill, a warmer house on the hottest days, and more wear on the compressor, which is the most expensive part to replace. A clean coil is one of the cheapest ways to help the whole system last.

How to do it

1. Turn the power off. Set the thermostat to off, then pull the disconnect or flip the switch in the box on the wall next to the unit (or the breaker).
2. Clear away leaves, sticks and weeds from around the base.
3. Rinse the fins with a garden hose on a gentle setting. Spray straight in, not at an angle, and work from the top down. If you can get to the inside safely, spraying from the inside out pushes dirt out the way it came in.
4. Never use a pressure washer. The fins bend flat easily, and bent fins block airflow just like dirt does. A cheap fin comb from the hardware store will straighten any you find bent.
5. Let it dry for a bit, then turn the power back on.

Recommended maintenance plan

Monthly (while it’s running):

• Check the furnace filter. Central air uses the same blower and filter as the furnace, so a clogged filter hurts your AC too. See How Often to Replace a Furnace Filter.
• Walk past the outdoor unit and pull any weeds, leaves or clippings building up around it.

Spring (before the first hot day):

• Hose off the outdoor unit as described above.
• Keep about 2 feet of clear space around it. Trim back bushes and don’t stack anything against it.
• Make sure the unit sits level on its pad.
• Flush the condensate drain line by the indoor unit with a cup of plain white vinegar so it doesn’t clog with algae and back up water.
• Run the AC and make sure it’s blowing cool air before you actually need it.

Mid-summer (if needed):

• A second rinse if cottonwood season or mowing has coated the fins.

Fall:

• Clear out fallen leaves. If you want to cover it for winter, cover only the top (a piece of plywood weighted down works). Wrapping the whole unit traps moisture and gives mice a nice place to move in.

Once a year, call a pro:

• Have an HVAC tech do a tune-up, ideally in spring before the busy season. They check refrigerant levels, test the capacitor and electrical connections, clean the indoor coil, and catch small problems before they turn into a breakdown in July. Anything involving refrigerant or the wiring inside the unit should be left to them.

Bottom line: one good rinse every spring, a filter check every month, and a yearly tune-up from a pro will keep most systems running well for a long time.