How to Clean AC Units: The Art of Maintaining Your Cooling Companion

Summer afternoons have a way of revealing truths about our relationship with technology. When that familiar hum of the air conditioner stutters or the cool breeze turns tepid, we're reminded that these metal boxes perched in our windows and mounted on our walls aren't just appliances—they're the unsung heroes of modern comfort. Yet most of us treat them with benign neglect until they wheeze their last breath on the hottest day of the year.

I learned this lesson the hard way during a particularly brutal August in 2019. My trusty window unit, which had faithfully served me through five summers, began making sounds reminiscent of a congested walrus. The culprit? Years of accumulated dust, pollen, and what I can only describe as a small ecosystem thriving in the fins. That experience sent me down a rabbit hole of HVAC maintenance that transformed my understanding of these machines.

Understanding Your AC's Anatomy Before You Start

Before you grab that screwdriver and spray bottle, let's talk about what you're actually dealing with. Air conditioners, whether they're window units, split systems, or central air, operate on surprisingly simple principles. They're essentially sophisticated dehumidifiers with attitude. The refrigerant cycles through coils, absorbing heat from inside and dumping it outside, while fans push air across these coils.

The components that need your attention are straightforward: filters (the lungs of the operation), evaporator coils (inside), condenser coils (outside), fins (those delicate metal strips), and drainage systems. Each plays a crucial role, and each collects its own special brand of gunk.

Window units are perhaps the most approachable for DIY cleaning. Everything's contained in one box, making access relatively simple. Split systems require a bit more gymnastics—you'll be dealing with an indoor unit (usually mounted high on a wall) and an outdoor unit that's probably surrounded by whatever landscaping seemed like a good idea three years ago. Central air systems... well, they're a different beast entirely, with components scattered throughout your home like pieces of an HVAC treasure hunt.

The Filter Situation: More Than Just a Monthly Swap

Everyone knows about changing filters, right? Wrong. The conventional wisdom of "change it monthly" is about as useful as a chocolate teapot in many situations. Your filter replacement schedule depends on factors nobody talks about at the hardware store: pet ownership (cat hair is particularly insidious), local air quality, whether you're a windows-open person, and even your cooking habits.

I've found that holding a filter up to the light tells you more than any schedule ever could. If light struggles to pass through, it's time. But here's what most people miss—filters aren't just about airflow. A clogged filter forces your system to work harder, sure, but it also allows dust to bypass the filter entirely, coating your coils in a fuzzy blanket of inefficiency.

For window units, the filter usually slides out from the front after popping off a plastic grille. Give it a good vacuum first, then wash it in warm water with a drop of dish soap. Let it dry completely—and I mean completely. Installing a damp filter is like inviting mold to a pool party in your AC unit.

Central systems typically use disposable filters, though some eco-conscious folks have switched to washable ones. Here's a pro tip that took me years to discover: write the date on the filter's edge with a Sharpie when you install it. Future you will thank present you.

Coil Cleaning: Where the Real Magic Happens

Now we're getting into territory that makes most homeowners nervous. Coils are where the actual heat exchange happens, and they're magnets for everything from dust to cottonwood seeds. Dirty coils can reduce your system's efficiency by up to 30%—that's like trying to cool your house while someone's following you around with a space heater.

For the evaporator coil (the inside one), you'll first need to cut power to the unit. I cannot stress this enough—electricity and cleaning don't mix well. On a window unit, the evaporator coil is usually accessible after removing the front panel and filter. For split systems, you'll need to open the indoor unit's cover, which often involves some creative positioning on a ladder.

Commercial coil cleaners work, but I've had excellent results with a simple mixture of warm water and mild detergent in a spray bottle. The key is to spray from the inside out, opposite to the direction of normal airflow. This pushes debris out rather than deeper into the coil. Use a soft brush (an old toothbrush works brilliantly) to gently work on stubborn spots.

The condenser coil outside requires a different approach. First, clear away any vegetation—I once found a bird's nest in mine, complete with extremely indignant occupants. Then, using a garden hose with moderate pressure, spray from the inside out through the fins. You'll be amazed at the mud that comes flowing out. Some people swear by commercial coil cleaning foams, but I've found that patience and water work just as well for routine maintenance.

The Fin Predicament

Those aluminum fins on your AC are about as delicate as butterfly wings and twice as important. Bent fins restrict airflow, making your system work harder and your electric bill climb higher. I've seen units where the fins looked like someone had gone at them with a comb in a windstorm.

A fin comb—yes, that's a real tool—can straighten bent fins, but it requires the patience of a saint and the steady hand of a surgeon. Work in small sections, and don't expect perfection. The goal is improved airflow, not aesthetic beauty. For severely damaged sections, sometimes it's better to leave well enough alone rather than risk making things worse.

Drainage Drama

Here's something that doesn't get enough attention: your AC produces water. Lots of it. That water needs somewhere to go, and when the drainage system clogs, you get everything from reduced efficiency to water damage that'll make your wallet weep.

Window units typically drain through a hole in the back or bottom. A piece of wire or a pipe cleaner can usually clear minor clogs. Some older units have a drain plug that needs periodic emptying—check your manual, or better yet, tilt the unit slightly backward to encourage drainage.

Split systems and central air have condensate drain lines that can develop some impressive clogs. Algae loves these dark, damp spaces. A wet/dry vacuum can suck out clogs from the outside drain, while a cup of white vinegar poured into the drain pan every few months helps prevent algae growth. I learned this after dealing with a ceiling that looked like a modern art installation thanks to water damage from a clogged drain line.

The Deep Clean Protocol

Once a year, usually in spring before the cooling season starts, your AC deserves a spa day. For window units, this means removing the entire unit (recruit a friend—these things are heavier than they look), taking off the outer casing, and giving everything a thorough cleaning.

I like to do this on a warm, sunny day in the driveway. Remove the casing screws carefully—they have an annoying tendency to disappear into other dimensions. With the guts exposed, you can really get at everything. Use a foam coil cleaner on both coils, letting it sit according to the manufacturer's directions. While that's working, clean the fan blades, check the fan motor for any signs of wear, and wipe down all surfaces.

The drainage pan deserves special attention during deep cleaning. Years of moisture can create some genuinely disturbing growths. A mixture of bleach and water (one part bleach to ten parts water) works wonders, but make sure you rinse thoroughly afterward.

Central Air Considerations

Central air systems present unique challenges because components are scattered throughout your home. Beyond the regular filter changes and outdoor unit maintenance, you should periodically check all your vents and returns. I once discovered that a previous homeowner had closed half the vents in an attempt to "save energy," essentially strangling the system.

The ductwork itself can harbor dust, mold, and the occasional surprise (I've heard stories of everything from love letters to cash stashes found during duct cleaning). While professional duct cleaning has its place, especially after renovations or if you notice musty smells, be wary of aggressive sales tactics. Not every system needs duct cleaning every year, despite what some companies might tell you.

When to Wave the White Flag

There's no shame in calling professionals for certain tasks. Refrigerant issues, electrical problems, or anything involving opening sealed systems should be left to certified technicians. I learned this after attempting to "fix" a refrigerant leak with hardware store supplies—a decision that cost me far more than a service call would have.

Strange noises deserve professional attention too. While some sounds are normal (the occasional pop or click as metal expands and contracts), grinding, squealing, or rhythmic banging usually indicate problems beyond the scope of DIY maintenance.

The Payoff

A well-maintained AC unit doesn't just run better—it runs cheaper and longer. My current window unit is pushing eight years old and still runs like it did on day one, thanks to regular cleaning. The hour or two spent on maintenance each season pays dividends in comfort, efficiency, and avoided repair bills.

There's also something deeply satisfying about understanding and maintaining the machines that keep us comfortable. In an age where so much technology is sealed away in black boxes, being able to open up an AC unit and actually fix something feels like a small victory against planned obsolescence.

Remember, every AC unit is slightly different. What works for my 12,000 BTU window unit might not apply to your multi-zone mini-split system. But the principles remain the same: keep it clean, check it regularly, and don't ignore warning signs. Your future self, sweating through a heat wave, will thank you for the attention you pay today.

Authoritative Sources:

"Residential Energy: Cost Savings and Comfort for Existing Buildings." 6th ed., by John Krigger and Chris Dorsi, Saturn Resource Management, 2019.

U.S. Department of Energy. "Maintaining Your Air Conditioner." energy.gov/energysaver/maintaining-your-air-conditioner

Environmental Protection Agency. "A Guide to Energy-Efficient Heating and Cooling." EPA 430-B-09-008, 2009. epa.gov/sites/production/files/2014-06/documents/guide_to_energy_efficient_heating_and_cooling.pdf

ASHRAE. "Standard 62.2-2019: Ventilation and Acceptable Indoor Air Quality in Residential Buildings." American Society of Heating, Refrigerating and Air-Conditioning Engineers, 2019.

Rutkowski, Hank. "Manual J Residential Load Calculation." 8th ed., Version 2, Air Conditioning Contractors of America, 2011.