Your unit exhausts into a crawl space? Doh?

Were these installed by a professional?

You have a window air conditioner which is designed to be installed in a window opening. It is designed to reject heat to the outdoors. You have it installed so that it rejects heat to an attic knee wall space--not a "crawl space." From the photos, it appears that the underside of the rafters has drywall or plaster installed. I'm guessing that insulation is installed in the rafter bays and vented in each bay via a baffle. If that's the case, then there is no air circulation in the knee wall volume because it's inside the conditioned building envelope. So your air conditioner rejects heat until the temperature inside the knee wall volume is too high to reject additional heat and it shuts down. You don't have a defective unit, you have a defective installation.

Thank you for the replies.

To respond to the comments above, the installation was done by my roommates - it just consisted of cutting the proper size hole in the wall, placing the air conditioner inside, and sealing any gaps with insulation & foam. The electrical work, however, WAS done by a professional - a licensed electrician - which included creating a dedicated 220 circuit for this ac since it uses 220 not 110. The electrician also ran the small duct, and installed the exhaust fan that you see in one of the photos.

.

Based on the last comment above, it sounds like the exhaust fan that was installed isn’t adequate. Could this problem be solved if a much larger, more powerful exhaust fan was installed?

.

This is the fan that’s currently installed - 100 CFM. Likely not powerful enough.

.

.

.

.

Perhaps a fan like one of these is needed, with a much higher CFM? Wouldn't a powerful fan like one of these solve the problem by allowing much more air to escape, and proving a consistent flow of air? Thank you for your insights, and taking the time to comment.

,

Seriously, Air conditioning is the transfer of heat.

Doesn't matter if it's a window unit or any other kind, PTAC, mini split, etc.

To transfer heat from a hot room to another area? heat does not transfer well into a hotter area.

If heat does not transfer well into a hot area, what do you think that compressor is doing and why?

Window unit = designed to put into a window. If you break the design it's not going to work.

Work? do what it was intended to do, from the manufacturer of the unit.

But the electrical was done professionally. -- excuses don't cure design deficiencies.

I service the Katy, Texas area... it will work, it will cost real money, backed up by IT WILL WORK.

(This ain't it)

You need adequate air flow through the knee wall volume to keep the temperature low enough for the air conditioner to work. I suspect you have a fan exhausting air from the knee space without a dedicated supply of outside air to the space. If that's the case, air flow will be minimal (limited to whatever the fan can pull through cracks and openings) and the system will operate as you described. You would need to adequately ventilate the knee wall space. However, doing so will bring hot, humid outdoor air into the space with the potential for mold and mildew.

Ductless mini-split heat pumps are designed for your application. Installing one will be more expensive than your window unit, but it's what you need to make the room habitable and not introduce unintended consequences that may result from your current approach.

What's the second photo of?

"One end of room has a slanted skylight, other end has sliding glass doors to a small deck"

Reduce the room's heat buildup before trying to ride the room of the heat buildup. Window film can help tremendously with reducing solar heat gain.

"Ductless mini-split heat pumps are designed for your application"

That would seem to be the solution. There are also through-the-wall and PTAC air conditioners.

The OP seemingly read the replies re no heat being removed from the attic knee wall area... and then ignored the info and focused on installing a larger fan.

To the OP: cold doesn't reallly exist in physics; it's just a word we use to describe the absence of heat or lack thereof.

Air conditioners do not "make cold". They merely take heat from one area (in this instance the air inside the room) and transfer it to another area (in this instance your knee wall space). When the temperature inside the knee wall space gets close to the temperature of the outside coil of the air conditioner, it no longer can transfer heat from your bedroom to the knee space, and sensors inside the unit shut it off to protect the compressor.

Feel the amount of wind produced by the unit's fan through the front grille when it is working; that's roughly the amount of air that needs to be removed from the knee space in order for this setup to work. And as others have mentioned, that air must be replaced with air from another space otherwise the fan will just keep on turning without moving any air and eventually it will burn itself up.

If you want to still use this unit, it must be installed through an outside wall where heat can be disspiated in free air outside.

If this room has no outside wall, the mini-split option proposed by other posters is the only viable solution.

Again I appreciate everyone’s comments. For what it’s worth, this setup was attempted because everyone in my house is disabled & dealing with a number of health issues. Money is short, help & family support are nonexistent, and since the central AC system died, and since we don’t have the resources needed to replace it, this is what we came up with. The excessive heat & humidity make us sick, and we are desperate to escape the heat. This particular bedroom has no “normal” windows to place a window AC unit. One end of the room has a slanted skylight, the other end has sliding glass doors to a small deck, so options are greatly limited, which is particularly unfortunate since it’s an attic bedroom that gets brutally hot.

.

Here are a few more photos taken today. I added a fan in the knee wall space to help increase air circulation. Before you jump all over me LOL, I know this isn’t a solution - I only did it hoping it will help for now, even if just a bit.

.

What I’d like to know is if a large, powerful exhaust fan were installed, wouldn’t that solve the problem? Seems it would, at least in theory. A much larger fan would provide an ample escape route for the hot air, and with the power of the fan pumping the air out at a fast rate, the hot air would be expelled so fast it wouldn’t have a chance to accumulate & be trapped, so the AC unit wouldn’t be choking on stagnant hot air. Am I missing something?

.

And when I was browsing through the many different exhaust fans out there, I saw some that are “reversible" - they both exhaust the air & intake the air depending on whatever the needs are at any given time. So wouldn’t that solve the problem of both expelling the hot air being discharged from the AC unit, AND providing ventilation by pulling in cooler, dryer air in during the cooler seasons to combat excessive heat & humidity?

.

I should also mention that I’m located in the northeast, so the AC isn’t needed year-round like in southern states. We mainly need the AC June, July & August. Right now unfortunately we’re having a severe heatwave - mid-90’s today, and 100 forecast for tomorrow with high humidity - so AC units all across the region will be working hard.

.

I really appreciate everyone’s comments & advice.

.

which is particularly unfortunate since it’s an attic bedroom that gets brutally hot.

I get why people attempt things like this. (lack of money for whatever reasons) .

So I use a sentence top line that you wrote... to explain.

The AC does not create cool, it merely moves heat from one place to another. But to move heat the best way, most efficient way (it has to be efficient or you get the power bill and?)

The heat is brutal... so moving it around isn't brutal? Efficiently is moving heat from hotter to cooler. Let's say you have 115F air being blown out the back, but the temp in that space is 120F or even 116F... it can't transfer heat under those conditions. (Heat moves from hotter to cooler, NOT hot to hotter)

To put this into efficiency terms: In a well-functioning air conditioning system, the condensing temperature is generally 15-20°F warmer than the outside air temperature. This temperature difference, known as the condensing split, is crucial for efficient heat rejection from the refrigerant. While a 20-degree difference is a common target, modern, high-efficiency systems might have a smaller split, potentially around 10-15°F

Putting a fan in there to blow that air around? The problem is the temperature of the air, fans don't lower that temp.

AC is a science box, it works based on science principles, doesn't care if you are broke or not.

The hotter it gets, the worse it gets. If it wasn't in an attic maybe... but that heat doesn't relent until the sun goes down at night, and it can take many hours for an attic area to cool down once the sun sets.

The fans you put in there are just swirling hot air around. If it doesn't change the temperature in this area it's not going to work. If you get it to work marginally, the electric bill over time will be another factor to be concerned with.

Are there vents on both sides of your attic knee wall area? If you had a large enough vent and fan on one side expelling air and a large intake vent on the other side to draw in enough air you could create the equivalent of the outside in your space. Its not visible in your pics where the air comes from and goes out.

Another option would be to open the slider enough to mount AC there and put rigid insulation above and below held in place by the slider with a dowel in the track to keep it snug against the AC and insulation. This isn't a pretty option but it would be cheap and relatively easy to do.

The OP related that the room is a bedroom without windows. Emergency egress is required by code in bedrooms. If there are no windows, then the (operable) slider is required to meet the emergency egress requirement.

Can you get a portable unit and vent it through the slider with a sliding door kit.

When you say the central AC died, did it just stop working and you figured it would cost too much to fix it, or did you have an HVAC technician look at it who then said the system is not fixable, or would cost too much money to fix it?

I don't know what is wrong with your central AC system, but if you didn't have it checked by a technician, you should find a technician who will give you a free estimate, or charge a minimal fee. It might turn out the repair is cheaper than it would cost you to make your window air conditioner contraption work.

Charles Ross Homes: "The OP related that the room is a bedroom without windows"

He wrote, "One end of the room has a slanted skylight, the other end has sliding glass doors to a small deck"

But his "solution" seems like Looney Tunes. He spent $1000 on that window air conditioner and more for the electrical circuit but didn't write that he'd hired anyone to check out the central AC. For the life of me, I can't figure out what that space with the purple rug is. Is that the "crawl space" with a door to a room with the clothes in the second photo?

Again, much thanks to everyone’s replies & helpful suggestions.

.

I will respond to the various questions & comments.

.

BEDROOM WINDOWS: The bedroom we’re trying to cool is a third floor attic bedroom & it DOES have windows - it just doesn’t have “normal” windows - the typical kind of windows that can accommodate a window AC unit. The attic bedroom only has a slanted skylight at the front end of the room, and a sliding glass door to a small deck off the back end. The only “normal” window is located in the bathroom, which is incorporated inside the attic bedroom, and there’s already a portable AC unit there, but it’s a huge obstruction in the tiny bathroom. Obviously a big, bulky AC unit in a bathroom like that is far from ideal as it’s a huge obstruction. And even at 12,000 BTU’s it’s struggling to keep up with this brutal heat.

.

VENTILATION: someone suggested perhaps putting a large exhaust fan into one end of the knee wall to suck out the hot air, then an intake fan on the other end of the knee wall to suck in the fresh outside air. Problem is that this property is a DUPLEX, so one entire side of the house is attached to the adjoining duplex. Therefore the only option I’d have for dual venting is the exhaust fan on the side of the house, where the existing small fan is (as seen in photo), and perhaps a roof vent for an intake fan. Or perhaps vice-versa; the exhaust fan on the roof, and the intake fan on the side of the house. I just need a viable plan ASAP because this extreme heat is killing us. It’s almost midnight here & it’s still 85 degrees outside! And that's after a hellish day where it hit 102 today! We broke records all across the region here. It's brutal. There have been all kinds of heat-related emergencies. I cannot fathom how people down south handle this kind of heat & humidity so many months of the year. I also don't know why so many people here in the northeast flock to Florida & other southern states. At this point, Canada is looking better & better!

.

CENTRAL AC: someone asked what happened to the central AC. Problem is that it’s not only broken, it’s a 25 year old system, and it has been on life support for the last few years, with more & more problems. Now it’s at the point that it can’t be revived anymore. Plus the freon is getting harder & harder to obtain, and since it’s becoming obsolete, it’s more & more expensive. We did have an HVAC guy look at the system last year & again a few months ago, and it’s officially dead. My housemate, who’s fairly handy & good with fixing certain things, even replaced the capacitor a couple of months ago as more of a “Hail Mary,” hoping it would revive it, but nope. A 25 year old system is toast, and with the many thousands it would cost to replace the entire system, it’s cost prohibitive for a household of disabled folks barely surviving.

.

PHOTOS: someone asked what that room is with the purple rug - it’s the knee wall space.

.

And yes, the solution is seeming more & more “Looney Tunes” as someone said because we have zero help, no one to turn to for help, and can’t afford multiple professional consultations, so we’ve been researching on our own for answers because we’re getting more & more desperate with this extreme heat, so we’re trying almost anything.

.

Again, thank you to everyone who responded. Your insights are much appreciated. I'd love to hear what any of you think about whether a dual-venting approach in the knee wall area would solve the ventilation problem. If a powerful, high-CFM exhaust fan AND a powerful INTAKE fan were installed into the knee wall space, wouldn't THAT create enough air flow in & out to make the wall AC work properly? I'd just need to know the ideal location for the fans. Would it be better to do the exhaust fan on the side of the house, and the intake fan on the roof, or vice-versa; intake fan on side of house, and exhaust fan on roof? And how high of a CFM fan should I be looking at? I've seen some comments saying it should be pretty high - like 1200 to 1500 CFMs.

Just to make myself clear, you don't only need airflow in the knee wall space, you need the actual TEMPERATURE inside the knee wall space to be significantly LOWER than the temperature of the coil, or grille, of the air conditioner on the knee wall space side. A 24K BTU air conditioner will make the temperature of this knee wall space rise pretty quickly and you need a way to dissipate that HEAT, away from the room you're trying to cool, and away from the air conditioner itself.

Again, thank you to everyone who responded. Your insights are much appreciated. I'd love to hear what any of you think about whether a dual-venting approach in the knee wall area would solve the ventilation problem.

The problem is heat, and to fully realize this you need to know what that actual temperature is in that knee wall area. Especially at the height of the day typically between 3pm and maybe as late as 7-8pm at night (under heat wave type problem).

If it's like I think it might be... say 115F or warmer in there where the heat transfer of the condenser of the window unit, not in a window is at... I don't know that you will ever get that temperature low enough to work right. This temp in the attic knee wall area will climb and at that same time is when the greatest load is being placed on that room you are trying to cool.

Radiant heat beating down on that roof, that heat is probably going to be too much to over come for just blowing air thru it.

Mikey Pipes on Youtube has a philanthropy for this kind of thing. So maybe you contact him see if he might be able to help you. He's out of Woodmere, NY but he's done philanthropy work with others willing to help in other states. (click here Mikey Pipes Philanthropy)

Thank you again to everyone who responded. I’m still struggling with this, and will probably end up aborting the entire plan & moving the air conditioner. This won’t be ideal since there are no “normal” windows to work with. I’d have to move it to the next closest window, to the room, which unfortunately is at the bottom of the stairs, so it will be less effective in cooling the room we want cooled.

.

Considering everyone’s comments about the importance of ventilation, and needing both intake & exhaust fans which are powerful (high CFMs) in order to get the AC to work properly if it’s vented into a knee wall area, I’m assuming I’d have to get an exhaust fan like this (see photo) with 2000 CFMs, AND an intake fan like this (see photo) with 2200 CFMs. What I’m unsure of is a couple of things:

.

1) Could I put both of these fans on the SAME side - like next to each other on the side of the house? The reason I ask this is because the house is a duplex, so I don’t have two sides of the house to work with to create a cross-breeze - the other side of the house is connected to the adjoining duplex - so the only other route I could go is through the roof, and I’m trying to avoid screwing with the roof.

.

2) If you look at the photo, the intake fan is also an exhaust fan - it can do both - so would that ONE fan suffice if I just switched it back & forth from intake to exhaust periodically, or is that not an option with this setup?

.

If I’d be forced to start cutting holes in the roof, I don’t think this will be a viable path to pursue since roof work is typically expensive, not to mention the disruption, and the chance for leaks & roof damage when holes are cut in roofs. And if you were to ask me what type of roof ventilation I currently have, I don’t even know. I’d have to do some digging to find out. But whatever it is, it’s clearly not adequate to support the setup of an AC in the knee wall space.

.

3) Would installing an exhaust fan ONLY in the knee wall space be a good idea just in GENERAL - regardless of the AC-in-knee-wall-setup - for the sole purpose of expelling hot, stuffy air from the top floor, which I'm assuming would help lower the temp on the top floor on hot days? Or would that not be the case if the exhaust fan were installed in the knee wall area which is sealed off from the finished, living space?

.

And lastly, with regards to the comments about how the temperature in the knee wall space needs to be significantly lower than the temperature of the coil or grille of the AC inside the knee wall space, I don’t see how that would even be possible, particularly on very hot days like we had last week where it reached over 100 miserable degrees. It was roasting in that knee wall space, as surely every attic space in the entire region during that brutal heat wave, so even with intake & exhaust fans, how would the heat be overcome? In other words, an exhaust fan would be expelling the hot air that has accumulated in the knee wall space, and the intake fan would be sucking in fresh outside air, but on those scorching hot days, the intake air would be brutally hot & humid. So on hellishly hot days, wouldn’t the whole system just be replacing hot air with MORE hot air? And wouldn’t this problem exist even if the AC were mounted in a window & vented outside? On a scorching hot day where it’s near 100 degrees, the outside air itself would be hot & stuffy with the high humidity, so even when it’s vented outside, wouldn’t THAT kind of high heat & humidity cause the AC to struggle?

.

Here's what I think will work for maximum cooling in your circumstances. Open the sliding glass door. Place the AC unit in the opening. Use an extension cord rated for 220v AND with the gauge required to reach the outlet you had installed for the first location. Use cardboard or foamboard for testing to fill the open space above the AC unit. Get a weatherproof replacement material once you're happy with the performance in this new location. Call your city about assistance in getting your central unit working.

Incredible! lol

3) Would installing an exhaust fan ONLY in the knee wall space be a good idea just in GENERAL - regardless of the AC-in-knee-wall-setup - for the sole purpose of expelling hot, stuffy air from the top floor, which I'm assuming would help lower the temp on the top floor on hot days? Or would that not be the case if the exhaust fan were installed in the knee wall area which is sealed off from the finished, living space?

I doubt it would work, so much so I wouldn't do it. In this business you have to know when to walk away and when to run. Trying something like this I would be running.

To exhaust air effectively you have to replace the air that you are exhausting. Air in = Air out.

When it's hot you're pulling in hot air from outside, but less hot than the air you are expelling.

The only way you could be confident it would marginally work is knowing what the temperature of that attic knee wall area is. If it's 100F at the start of the day, likely get gradually worse by heat of the day. Once you start hitting temps of 110F and higher the compressor will just shut off.

Have you measured what the actual temperature is in that attic knee wall area is during heat of the day?

However, with exhaust only you have radiant heat beating down on that structure... so on a hot day you would have heat transferring to the air you pull in from outside not just from the AC condenser from the window unit that is not in a window. This will all have a bearing on the outcome. I know better if I am some how not making this clear?

Would this temp of the attic space knee wall be low enough for the window unit, not in window for this window unit too work and cool off an attic room that is also under stress from the heat.

My guess is no. There are reasons why things are designed as they are. The cure for design issues is to rip it all out and start over. You're trying to redesign the use of a window unit. I think we understand why you are doing this, but that doesn't mean it will work. (work means cool an attic room while over coming design issues to boot).

You don't have to be a building science expert to know that a sufficiently large exhaust fan exhausting air from the upper floor of a building will pull air from the lower levels and enhance comfort. They're called whole-house fans. The problem is the required air flow rate is high--the fan you'll need will be large, noisy, and turn your air conditioning issue into one for your housemates on the lower levels. Sharing is not always caring.

Solution #1. Put the window AC unit in the sliding door as dan described, with “something” blocking off the rest of the door opening above the AC unit. The something can be doubled-up cardboard boxes taped to the wall, to see if it works, then get some corrugated plastic (hardware store, left-over yard sign) or other longer-lasting material. Kind of a temporary solution, just because it will look like heck and partly block the sliding door.

Solution #2. Sell window unit, buy a portable AC unit with two hoses, install hoses in skylight (if it opens) or sliding door (similar to above). Portable units are designed for this application, run on 120v (though if there’s anything else drawing a lot of power on that circuit, like microwave or electric kettle, may trip breaker), won’t drip condensate on the floor. Not as powerful as the window unit though will look better.

Solution #3. I’m sure someone could devise a solution that uses one fan to pull air from kneespace to outside and another fan to pull replacement air from outside into the kneespace, at a high enough rate to keep the kneespace temperature similar to the outside temperature, so that the window AC will work. The kneespace is only, what, 200 cubic feet? Shouldn’t be too hard to replace that volume of air every couple minutes. Yes you’ll be bringing moisture into the kneespace, but you’ll be pulling it out too. Honestly that probably is what I would try to do. I would use sheet metal duct, not that flex stuff. But it may be more work than you want to tackle when it’s freaking hot. Maybe save that for the fall.