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Community and Q&A

Improving the Performance of an AC Window Unit

etting | Posted in Mechanicals on

My 12.200 BTU window air conditioner runs well until the outdoor temperature here in central Arizona hits around 105, at which point it trips the 15-amp breaker, and I shut it off till the evening, when it’s fine again.  Everything is clean and undamaged, and nothing else is running on that circuit.  Normally 105+ days are fairly rare here, but we’ve had a bunch already, and it looks as if a bunch more are on their way.

It was suggested in another discussion here that an evaporative cooler’s output, directed at the condenser coils outdoors, may improve a window AC’s performance. I’m sitting by a big, portable one inside the house to get by, but if I get more than a few feet away, the house is miserably hot.   It’s probably too big to mount outdoors at the height of my window AC, but one of those little ones that seem to be advertised everywhere would be pretty easy to mount, and some of them have a reservoir that lasts for several hours.

The best reference I found on this idea is at, which says, “A real air conditioner is used to test the innovation by putting two cooling pads in both sides of the air conditioner and injecting water on them in order to cool down the air before it passing over the condenser. The experimental results show that thermodynamic characteristics of new system are considerably improved and power consumption decreases by about 16% and the coefficient of performance increases by about 55%.”

I’m not sure I can duplicate the setup they describe, so I’m wondering how much good a little (foot or so tall) evaporative cooler might do to keep my window AC from overloading its circuit on 105+ degree days.

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  1. walta100 | | #1

    Before you start modifying things have you dissembled and clean the coils?

    Is the 15 amp breaker that pops in the circuit panel or is it on a power strip?

    Most window units are designed to have the outdoor coils cooled with the condensate water from the indoor coils. It seem unlikely your coils get much if any water from condensate in AZ. Once you have clean coils.

    I see no problem if you were to pour a cup of water every half hour into the units indoor drain so it will flow outdoors and be sprayed on the coils by the unit

    Your circuit breaker should not be tripping this unit likely requires a 20 amp circuit to operate correctly.


    1. etting | | #2

      Thank you, Walta. I haven't disassembled anything, but the coils look quite clean. The breaker is tripping at the panel. I expect a 20 amp breaker would not trip, but the plate on the AC says to use a 15 amp. It never tripped until this summer's excessive heat. Great suggestion to pour water from indoors!

      1. charlie_sullivan | | #3

        It might be worth getting a kill-a-watt brand meter to determine how much current you are actually drawing. It might be that the breaker needs replacement and is tripping earlier than it should. That will also help you monitor whether the simple solution of pouring a little water in works.

        1. etting | | #6

          Thank you, Charlie. An aged breaker is a possibility worth keeping in mind.

  2. walta100 | | #4

    If the unit is more than a few years old I would guess it is overdue for a cleaning. Often you cannot see how dirty and clogged the coils are before disassembly.

    If the AC was tripping the breaker because it was working too hard IE overloaded the units internal overload should trip and shut the unit down until it had cooled off and then it would restart.

    If the unit uses more than 12 amps code says it must be connected to a 20 amp circuit.

    Is there an extension cord in the circuit? Anything else go off with the AC?

    Note the circuit breaker is not designed or intended to protect overloaded or failing appliances from damage they are required to have internal circuits for that porpoise.

    The breakers sole job is to prevent the wire in the wall from overheating and being damaged.


    1. etting | | #5

      Thank you, Walta. I understand the purpose of the breaker. The unit specifies a 15 amp breaker. It trips with nothing else running on the circuit and no extension cord. I will look up how to disassemble it and clean any hidden dirt. Thank you for that suggestion.

      I tried pouring some water but apparently not enough. I didn't want to overdo it and have water spill onto something it shouldn't. My unit has kind of an open tray for the condensate, around 2" x 2" of which I can reach with a narrow bottle.

      I read an interesting article here on GBA about the Mistbox, a device that mists the condensing coils on a window AC. The author wasn't very impressed, in part because the thing uses around 32 gallons of water per hour, by her estimate. That may indicate that my pouring effort fell vastly short.

  3. Expert Member
    BILL WICHERS | | #7

    Yes, your idea will work. I have done this on "drycoolers" before at work. Drycoolers are basically big radiators used to cool a glycol loop for air conditioning systems. We used sprinklers to continually mist the coils, which got us about an extra 10*F margin on the system -- sufficient to increase cooling capacity on particularly hot days. We jokingly called the spinklers "afterburners" . It uses a LOT of water, so keep that in mind. The down side is that water rots out the aluminum cooling fins much faster, so there is a tradeoff.

    With really hard water, you will get scale buildup on the coils which will actually reduce your cooling capacity over time, so be aware the water mist system is not without risk.

    I agree with the other posters that cleaning your condensor is a better first step. Water mist shouldn't be tried before cleaning, eithere, because the water mist can actually force the dirt further into the coils where it is harder to remove. I recommend carefully using a vacuum cleaner to suck out as much of the dirt as you can -- especially tree fuzzies -- then use water to wash the coil out. If the coil is particularly dirty, you can get coil cleaning solutions but they are corrosive and eat away a little bit of the cooling fins every time you use them, so you should minimize your use of these cleaning solutions as much as possible.


    1. etting | | #8

      Thank you, Bill. I do have very hard water and was leaning away from spraying it on the coils. I was thinking a small evaporative cooler's output would be safer, but given how much water it takes to achieve cooling, I'm surmising that a little cooler wouldn't do significant good.

      I just watched a YouTube video where someone cleans her condenser coils without removing the unit from the window: It's quite long but can be summed up pretty easily as spraying a solution of liquid Castile soap and water through the outdoor fins, then pouring water through the vents to rinse the dirt out the bottom drain holes. My AC would be difficult to remove, so I'd prefer this method if it's reasonably effective. What do you think?

      1. Expert Member
        BILL WICHERS | | #9

        Evaporative coolers can be very effective in areas with low humidity levels. In the Denver area, for example, the utility even offers rebates for them. The tradeoff is you use lots of water instead of electricity. If you're in an area with higher average humidiy levels (like SE MI where I am), evaporative coolers can actually make things worse, since they humidify the air they cool, leading to muggy conditions in humid areas.

        I would use purpose-made cleaners for the coils if I used any cleaner at all. I normally use no cleaner. Commercially, we clean the coils with cleaner maybe once a year, and the coils on these coolers run 24x7 all year long. For "regular" cleaning, we load the coils with water, then let the water drop out (we can cycle the fans, and the coils are horizontal), which tends to pull out dirt with each "drop". On vertical coils, I spray water in a top-down pattern, following the fins to work the dirt out. Ideally you want to spray water from the inside to the outside, in the opposite direction of air flow to push out dirt. Vacuuming first helps since it gets out the easy dirt that otherwise gets stuck when it gets wet, making it harder to remove.


        1. etting | | #10

          Thank you, Bill. My big evaporative cooler is doing a decent job of keeping me from overheating inside the house when my AC trips the breaker. To be clear, do you think a small (around 12" high) one could significantly improve the performance of my window AC by cooling its outdoor coils, mounted several inches away from them?

          It seems to me one of the AC makers could gain a market advantage by making much of the bottom of the outdoor part removable to facilitate cleaning.

  4. thegiz | | #11

    Are you running just the AC? Inexpensive fans could help with overall cooling along with the AC, especially ceiling fans or anything that can circulate air. That would help in times the AC trips or not sure how this would work but it could limit the amount of energy the AC needs to produce to lower the temperature. More than one AC is also good but then you would be using a lot more energy.

  5. Expert Member
    Dana Dorsett | | #12

    Seriously, if it has hundreds or even thousands of hours on it there is going to be a lot of crap in the coils, usually more in the outdoor (condenser) coil than on the indoor coil, which has at least a bug & dog-hair type filter.

    Take it outside, pull the cabinet completely off, vacuum up all of the crud in the pan (taking care not to dent the coils), then take a soft bristled brush to both the indoor facing side of the outdoor coil and the indoor facing side of the indoor coil to remove any heavy matted stuff. (You may have to pull the fan to get at it.) While you're at it, scrape any crud that has accumulated on the edge of the blower/fan blades- it can get to be pretty heavily caked over time.

    Get a finger-pumped spray bottle and fill it with a solution of hand dishwashing liquid and spray both sides of the coils, then let it sit for a good 5-10 minutes, and repeat. Then take a hose with a spray attachment and spray through the coils from the outside in- (the opposite direction of the normal air flow.) Set spray attachment to a somewhat broad mist rather than a narrow hard stream to avoid bending the coils' fins. If you have any bent/bashed fins, carefully straighten out what you can using a purpose made coil brush. It'll never look perfect again, but restoring most of the air flow will help.

    After a good rinsing take a good look through the coil- you should see lots of daylight. Repeat the soapy water part if you see any residual clingy junk. (Pollen & airborne weed/tree seeds can be pretty gluey.)

    Don't worry too much about getting the electrical connections and control parts wet- don't soak 'em but if they get a bit wet it's not a big deal- just be sure to dry it out thoroughly before putting the cabinet back together.

    If it's STILL tripping the breaker (and not because the breaker is worn out) consider replacing it with an inverter-driven higher efficiency 1 tonner. The LG LW1517IVSM (14K- a bit bigger than 1 ton) or Midea MAW12V1QWT (12K) won't pull anywhere near as much peak current as your old school 1-speed because the compressor never cycles off (= no start-up surge) and the inverter driven compressor motors for the compressor and fan(s) are simply more efficient. The LG is rated 14.7 CEER, the Midea 15 CEER. Very few older 1 ton window units would have tested better than 11 even when shiny-new with perfectly clean & straight coils. Both of those units use the more enviro-friendly R32, with a quarter to half the global warming potential than R22 or R410A.

    The LG installs pretty much like other window-shakers, whereas the Midea has a U-shape that allows the window to slide down between the compressor side and the indoor side for better noise isolation. It's pretty hefty long front to back, and a bit awkward to install, and needs a lot of air sealing detailing around the mounting bracket that comes with it. It's in the second year of production- some of those issues have been dealt with, but not all. In many ways the Midea is just a "mini-split in a can", with the same functions & same remote used in several Midea & Carrier mini-splits. (It doesn't respond to "Heat" mode though, despite being displayed on the remote. :-) )

    List price on the LG is abut $550, list on the Midea is $460, but there has been limited availability and even some price gouging on the U-shaped window units, which comes in 8K, 10K, and 12K sizes. Street/internet price on the 8K size (MSRP ~$350) when you can find them is even higher than the 12K right now.

    A step up from there would be a DIY 1-ton mini-split, which is a whole other project, but can be quite a bit more efficient. A 110V 1-ton Senville or Pioneer with a 16' lineset can be had for under $800 if you shop around.

    1. etting | | #13

      Thank you, Dana, for lots of great advice, the range of options, and all of the model numbers, prices, etc., which are extremely helpful!

    2. Expert Member
      BILL WICHERS | | #14

      Dana, I've usually found a more direct and heavier stream to be more effective than the mist settings on a nozzle. You do have to be careful to keep the stream parallel to the fins though to avoid bending them. The more foreful stream is better at dislodging crud.

      BTW, I like your term "window shaker" for these window-mount A/C units :-)


      1. Expert Member
        Dana Dorsett | | #15

        >"I've usually found a more direct and heavier stream to be more effective than the mist settings on a nozzle."

        You're right of course.

        A lot depends on the nozzle, and the pressure/velocity of the stream. The point is start with a less focused stream, make it heavier as-needed to dislodge the crud while being mindful to not bend the fins.

        >"I like your term "window shaker" for these window-mount A/C units :-)"

        I didn't coin the term, but I like it too. Most are pretty noisy.

        I recently bought one of the 1-ton U-shaped Mideas to deal with a hot-spot in the house underserved by the central air. It's a ~120 square foot loft/landing at the top of the stairs in an antique bungalow, half of which is a flat 6,'8" ceiling , the rest an 8:12 sloped ceiling both with with R21 fiberglass in full dimension 2x6 rafters 16" o.c., and 18 square feet of west facing windows, and no supply duct. It has become the home-office, with the desks tucked under the sloped ceiling, printer, table filing cabinets on the taller area. Even though one of the 5000 BTU/hr (EER10.7) Frigidaires previously used to cool the upstairs bedrooms would have been more than enough to cool that space, they're annoyingly loud. High on the decision tree that got me to that model was the noise specs.

        At low fan the 1-ton Midea runs at an almost mini-split quiet 42 dbA, partly because it's using a scroll compressor and both the condenser fan & compressor are placed on the other side of the window. The compressor itself even has a sound abatement covering/blanket to help cut the noise. At higher fan speeds it's louder, but still not as loud as the smaller AC units.

        That said, it's still a window shaker. The sash that drops between the interior & exterior halves is by nature a tympanic surface with resonance frequencies. At certain speeds the modulating compressor it sometimes delivers a very low frequency (< 15 hz) hum, but it's not too intense, and quite tolerable. When quiet is needed for telephone calls, video conferences etc. setting the fan speed on Low rather than letting it modulate works fine, even with the unit 6' from my head.

        Nerd that I am, it's being powered through a Kill-a-Watt (tm) instrument. (At least I didn't put it on a data logger and use an app to track power draw against outdoor air temp using the Wi-Fi. :-) ) The modulation range turns out to be wider than anticipated. Under very light loads, with the compressor running continuously at it's lowest speed and both the indoor & exterior blowers modulating at low speed the power draw modulates nicely in the 85-100watt range. The nameplate max specs on it is 12.7A @ 115V which is a bit under 1500 watts. The only time it's been anywhere near max was the first few minutes after it was installed, when the room temp was north of 85F. The initial powerdraw was modulating between 1000-1200watts, but within 10 minutes it was under 8000W and falling. It could actually hit the high range again on days when it breaks 105F outside, but that pretty much never happens in this location. The southern edge of the room is an open baluster railing overlooking the kitchen, the thermostat for the central air is an open archway away from the east facing open stairwell to the living room. With the window shaker set at 73F, the central air set to 76F it ends up providing a substantial share of the cooling for the first floor via convection, even though it never reaches half of it's maximum.

        1. Expert Member
          BILL WICHERS | | #16

          Those scroll compressors 'wear in' over time, and may get a bit quieter. I've read about this, but never actually taken measurements myself. Most of the big commercial stuff I work with is either large piston-type compressors (carlisle units, mostly), or the turbine-type compressors used on the big chillers which are an entirely different animal. It would be interesting to take some sound measurements over time to see if there is any noticeable improvement after some period of operating hours.

          Have you considered a duct booster instead of a window shaker? I've had good luck with those in some circumstances, especially if they are left running all the time. Sometimes they help to equalize temperatures with airflow, such as in corner rooms that can be trouble spots.

          BTW, No loggers? How will you establish trends over time? We're going to have to work on your geek credentials ;-)


        2. aunsafe2015 | | #23

          How well does the Midea unit do at maintaining a steady set point? Say you have a setpoint of 76. Would the temp in the room range between, like 72 and 80? Or would it be a smaller range... perhaps more like 75-77?

          1. Expert Member
            Dana Dorsett | | #24

            >"How well does the Midea unit do at maintaining a steady set point? Say you have a setpoint of 76. Would the temp in the room range between, like 72 and 80? Or would it be a smaller range... perhaps more like 75-77?"

            With a setpoint of 73-74F the thermometer on the desk 7' away reads 71-72F, and does not vary by more than a degree from 6AM (when it might be cycling on/off at 100 watts) through the hot afternoon & evening at much higher modulation levels. The desk thermometer. is within the oscillation sweep of the output when it's in "Swing' mode, but offset, not directly in the main flow. The thermometer on the desk never reads higher than the programmed setpoint of the Midea, only lower, but by at most 2 degrees. YMMV.

            Like (most) mini-splits the window unit can only measure the room temp via the incoming air, so the configuration and air flows within the room near the air conditioner will affect temperature stability.

    3. aunsafe2015 | | #20

      Dana, do you have any knowledge of whether Midea plans to make a heat pump version of its U-shaped unit?

      1. Expert Member
        Dana Dorsett | | #25

        >"Dana, do you have any knowledge of whether Midea plans to make a heat pump version of its U-shaped unit?"

        I have no idea.

        My understanding is that this line was originally an Indiegogo funded product development. I suppose we could similarly fund an expanded features wish list that included things such as a heat pump mode and a "Follow me" function like they have for some of their mini-splits using a temperature sensor in the hand held remote for determining the room temp.

  6. etting | | #17

    I removed the unit from my window and removed the casing, sprayed the condenser fins with a solution of water and dish soap, let it soak for around 10 minutes, and rinsed with a garden hose. It seems to be performing better, although it's "only" 98 here today. The evaporator coils on the indoor side had a lot of fine dust packed between the fins that I hadn't seen until I got it out in the sun, but those fins were inaccessible from inside the unit without disassembling the internal parts, so I couldn't see a good way to rinse the dust out from the inside out. I've just read and watched ten or so articles and videos on cleaning a window AC, and to the limited extent any of them address cleaning the evaporator coils, they seem to suggest methods that, to my thinking, would push the dirt farther in, except for using a foam cleaner that supposedly pushes dirt out via its foaming action. Some suggestions above include using a vacuum for other purposes in cleaning. Would a fairly powerful vacuum combined with some gentle brushing to nudge the dirt loose work well to pull dirt out of the evaporator coils from the indoor-facing side?

    1. Expert Member
      BILL WICHERS | | #18

      You could try canned air to blast stuff loose. You want to blast in the opposite direction from regular airflow though, to ensure you don't just drive the crud deeper into the coils.

      Another trick I've used, but on massively larger units, is to load the coil with water while the fan is running, then shut off the fan so that the water drops out of the coil. A few cycles of that cleans coils pretty well. I don't know if that would work on a window shaker though.


      1. etting | | #19

        Thank you, Bill. Blasting canned air seems like a good idea, and I saw it recommended on several of the resources I checked, but on my window AC, the back (internal) side of the evaporator coils did not seem accessible without taking apart a lot more than the outer casing. Is that atypical, or if not, how can one blast canned air from the inside out?

        1. Expert Member
          BILL WICHERS | | #21

          If you can't get inside enough to blast them from behind, I would use a brush to CAREFULLY get the worst of the surface crud off, then blast at a very sharp angle to try to get stuff out. The goal is to blast stuff out of the coils without driving anything deeper inside.

          Do the best you can. You're bound to make an improvement, so it's a question of "how much better is it" and not "did I make it worse".


          1. etting | | #22

            Thank you, Bill. I just ordered a very inexpensive, but pretty powerful small vacuum with a brush attachment to try to pull the stuff out of the fins, and I'll report how it works. None of the resources I've checked or anyone here has recommended for or against that solution for the fins that can't be blasted with air or water in the right direction, so I'm looking forward to the experiment.

  7. Expert Member
    Dana Dorsett | | #26

    >"I just ordered a very inexpensive, but pretty powerful small vacuum with a brush attachment to try to pull the stuff out of the fins, and I'll report how it works."
    >"... those fins were inaccessible from inside the unit without disassembling the internal parts, so I couldn't see a good way to rinse the dust out from the inside out."

    Get whatever you can out dry with the vacuum, then try soaking with the soap solution sprayed from the accessible front side, and re-vacuum. It isn't as quick as getting it out with a rinse, but has to be better than a dry-vac alone.

    Depending on how dusty your indoor air is and the raw hours/annum it sees the evaporator coil might need to be cleaned every year or two to keep it running at or near it's rated capacity & efficiency. In my area (1% outside design temps in the low to mid 80s, ~500-600 annual CDD) cleaning the coils once per decade is usually enough. Last summer I cleaned the coils on a circa 1980 1-ton through-wall unit at a relative's house that hadn't been cleaned since at least 2010 (the year they bought the place), and it wasn't nearly as bad as anticipated- it cleaned up fine with just dry-vacuuming and a horsehair brush- no soap, no rinse. A decade of operating hours here amounts to roughly 1.5-2 years worth in places like Austin TX.

    1. etting | | #27

      Thank you, Dana. I wonder whether the advisability of a soap solution on the interior fins depends on how oily the dirt is. If it's not oily, I could see an argument against soap because of the residue it would leave behind, which might trap more dirt than bare metal fins, unless it could be thoroughly rinsed away from the same direction it was applied. If the dirt is oily, the soap would probably dissolve and thereby help remove much more oil than the amount of soap residue that would be left behind. In my case, the dust probably has as little oil as you would find in a house, as I never cook or use anything oily, but I'm sure there's some oil in the dust, as most household dust is shed skin cells.

      1. Expert Member
        Dana Dorsett | | #28

        Nothing is really perfect. While it would be nice to thoroughly rinse to remove any detergent residue, the benefits of the surfactants will in most cases outweigh the down side. Pollen (a likely component of the dust) can be quite sticky, but surfactants weaken the adhesion. Vacuuming out the bulk of whatever slurry is formed will lessen (but not completely eliminate) the detergent film left behind, along with the bulk of the insulative & air-impeding crud. Establishing and maintaining air flow is far more important than how thick the films of crud/detergent build up on the fins.

        1. etting | | #29

          Thank you, Dana. Seeing how much comes out with a brush and vacuum and then perhaps with straight water and a vacuum should give me a good sense of the dirt's oiliness/stickiness. If I need to get more out, I will use a soap designed to rinse away easily without leaving a residue, like some dish soaps according to their ads, and rinse it away as much as I can by spraying from the front.

  8. etting | | #30

    My new little vacuum with a brush attachment removed a fair amount of dust, but its brush wasn't nearly as effective as a nylon-bristled brush that looks a lot like a toothbrush, but with bristles around twice as long and not quite as densely packed. Brushes like this often come in a three-pack with steel-bristled and brass-bristled ones. I used a sort-of flicking motion by rotating the brush around its long axis so that it reached into the fins and then pulled the dust out as the bristles rotated outward. Without using water or a soap solution, I removed around 95% of the dust I could see with a very strong flashlight, which is essential to really see what's there. The fins looked pretty clean in regular room light, but actually held quite a lot of dust.

    It should hit 103 or so in a couple of days here. I'm looking forward to seeing how much better my AC performs. Thank you all for lots of great advice.

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