A few weeks back we showed you how to clean the indoor coil with foam. This is the other end of the system. The unit in the video is a gray two-ton solar hybrid that's been sitting against a wall out here in the desert.
Dave runs a finger across the top of the cabinet and can nearly write his name in the dust. Whatever is on the cabinet is probably on your coil, too. And the coil is where your unit gets rid of heat.
First thing: kill the power
Before anything comes apart, the power goes off. Turn off the breaker. If you have a 12,000 BTU unit that plugs into an outlet, unplug it. If yours is a solar hybrid, disconnect the solar as well. The unit in the video runs on solar only, so that's what we unplugged.
Dave mentions it partway through and again at the very end, after Todd reminds him. It belongs at the top of the list, so that's where we're putting it.
Decision one: clean it where it sits, or move it?
Most of the coil is on the back of the unit, and the back is usually a few inches from a wall. So you have a choice.
You can make the 80/20 decision: spray cleaner on what you can reach and call it good. That's a perfectly reasonable Saturday. Or you can do what we did and move the unit away from the wall so you can get at the whole coil. We're perfectionists around here. It was also a fair amount of work, and Dave says so.
What “self-rinsing” on the can means
We used a foaming coil cleaner in a spray can. The label says “self-rinsing,” with an asterisk. Dave reads the asterisk: it's self-rinsing on coils that produce condensate, and you may also wipe it clean or rinse it with water.
Your indoor coil makes condensate, so the foam drops into the drain pan and goes out the drain. The outdoor coil in cooling mode doesn't get that help. The foam is designed to lift the dirt and fall off on its own, which is handy if you're on a roof with no hose. We had a hose, so we rinsed.
A mini-split isn't a big central AC condenser
On a typical three-and-a-half or five-ton central air condenser, the electronics sit in their own compartment, away from the coil. People hose those down from every direction.
A mini-split is more compact. When Todd takes the top cover off in the video, the first thing you see is electronics: the main board and, on this unit, the solar board. They're enclosed, but you still don't want water anywhere near them.
So we didn't spray down through the top. We took the front grille off and worked through the fan opening, with the water pointed down and away from the boards.
Get the big stuff off first
Looking down at the coil from above, there were pigeon feathers. If you live near cottonwood trees, you already know what ends up on a coil. Foam cleaner isn't going to dissolve a feather. Pick or vacuum the loose surface debris off before you spray, or you'll be rinsing it deeper into the fins.
Spraying the cleaner
Most of the dirt is on the outside face of the coil, because that's the side the air comes in. That's where the cleaner goes first. Todd's recommendation is about eight inches away. Dave's is slow and steady. Both are right.
We sprayed from the inside as well. The coil on this two-ton unit is two rows thick, and if the fins in the two rows didn't line up, cleaner from one side might never reach the other. That's probably more than most people need to do. It's also only a few more seconds of spraying.
We didn't take the fan blade off. It's one bolt, and it would have made the inside easier to reach. It got by us in the planning. You'll get most of the dirt either way.
Then you wait. We gave it about five minutes. In a breeze the foam breaks down and drops off faster than that.
Rinsing: from the inside, angled down
Dirt went in from the outside, so you push it back out the way it came. Todd rinses from inside the cabinet toward the outside, holding the hose at roughly 45 degrees and pointing down.
He got a little closer to the electronics than Dave would have liked. Keep the spray low and away from that corner, and you're fine.
Why a cloudy, windy day is a good one for this
It happened to be both when we filmed, and Dave was pleased about it. Here in the desert the water is hard. If rinse water dries on the coil in full sun, the calcium stays behind on the fins.
The coil is your heat exchanger. Anything sitting between the metal and the air, whether it's dust or mineral scale, makes the unit a little less efficient. Clouds slow the drying and wind helps carry the water off. If you have neither, Dave suggests a shop vac set to blow.
Put it back together
Everything goes back in reverse order: grille, top cover, unit back in position, then power.
Your results will depend on where you live. We're cleaning off desert dust and the occasional pigeon. In Florida, where more things are alive, you may need a different cleaner or a different schedule. The decisions are the same ones, though: how much to take apart, where the water goes, and where it must not go.
If you're looking at your own outdoor unit and you're not sure what you're seeing, call or text us at (725) 699-1200. We build these. We're glad to help.
Haven't done the inside yet? Here's the indoor coil cleaning video.
