Turning a dumb AC unit smart (without losing my security deposit)

7/29/2026 at 7:44:57 PM

The "couple a stepper motor to a shaft" API is so much better than any "smart" appliance API.

Speaking more seriously, I wish classes of appliances would expose some simple analog and digital interface pins in a standardized configuration to let users choose whatever automation or monitoring hardware they want. HVAC equipment does this with standardized thermostat terminals. I'd love to see that on other types of appliances, too.

The manufacturer's crappy "app" that will inevitably be abandoned and require keeping some old phone / tablet in good "health" lest you lose the "smart" functionality (or worse, any use of) the appliance.

Then current way of putting the "smarts" inside the appliance is just planned obsolescence and a recipe for all of us being eyeball deep in ewaste.

by EvanAnderson

7/29/2026 at 8:21:36 PM

It always kind of blows my mind that I keep seeing "smart TVs" which have a bunch of integration options for high-end AV installations (rich people's houses, etc.) but no API that you can integrate with to just handle toggling channels/inputs/power states/volumes.

(I did get my last Sony Bravia integrated with Homekit so that I could control inputs, volume, etc. via the Home app, but that's not really what I'm looking for).

Give me an HTTPS API, require me to authenticate devices on the TV itself before it accepts their commands, and just let me do whatever. Default it to off and make it a hidden setting, but yeah just let me do the thing without having to pay tens of thousands of dollars for some professional installation to integrate with hardware I don't have and can't afford.

by danudey

7/29/2026 at 8:48:43 PM

Smart TVs don't exist for your convenience. They exist to track your behavior and serve you ads. If they happen to have some hackability, it's an accident or happy coincidence.

by dfxm12

7/29/2026 at 8:30:51 PM

It always blows my mind why those rich people even bother with TVs. I'm not rich by any measure, but still I can afford a projector, a screen and a couple KRK monitors.

by lstodd

7/29/2026 at 8:42:28 PM

Multi use rooms require TVs.

Projectors cannot handle ambient light without being a fire hazard.

by Guvante

7/29/2026 at 8:59:52 PM

>Multi use rooms require TVs

That seems an overstatement. I now have one in my entire house (don't have kids).

There's a fairly large TV panel on one wall in basically a sitting room. Otherwise I just use a computer. A relative basically has TVs in every room. I guess it maybe made sense when he was rebuilding anyway but it still seems excessive to me who might sit down to watch a movie or show but doesn't have live TV.

But, then, I don't have AC either in Massachusetts.

by ghaff

7/29/2026 at 9:04:32 PM

If you are rich you have single-use rooms. Hell, even I have a sleeping room, a cat room and a hacking room. It's not that expensive. The cat room doubles as a mini-cinema.

Ambient light is dealt with having nice thick blackout drapes.

This is not some rocket science, it was done for like a hundred years.

edit: actually in my former apartment I just bought a roll-down projector screen that completely covered the window. pull down - zero ambient light even in full sunshine.

by lstodd

7/29/2026 at 9:21:57 PM

Lots of people (even exceptionally wealthy ones) don't want to always have to go to the theater room to go watch something. Lots of people like having the TV on in the same way one might think about having a radio on, its not necessarily a thing they're exclusively focused on.

Take a look at this house:

https://www.zillow.com/homedetails/5619-Walnut-Hill-Ln-Dalla...?

Sure, it has a theater room with probably an incredible projector I'd imagine. It also has a bar with a big TV behind it. It also has a game room with several TVs mounted on the walls. In both of those situations, you wouldn't really want a projection setup. A brighter TV wins out in the end.

I've seen lots of TVs mounted in outdoor living room/kitchen arrangements. They're common to find in living rooms even for people who have separate theater rooms. I've seen them mounted in garages. TVs have uses other than just pure cinematic experiences. And I say that as someone who has personally pushed TV watching to an exclusive space in my home and made a point to not have TVs everywhere. Other people like different things.

by vel0city

7/29/2026 at 8:53:34 PM

When I had a kitchen fire, I told my electrician "no smart stuff" and he was happy to go along. (I had very little previously.) He did simplify and updated my electrical panel and switches which sort of accreted over time.

by ghaff

7/29/2026 at 9:13:53 PM

Nowadays it's surprisingly easy to vibecode replacements to some shitty OEM apps (and fix bugs while you're at it). I've had pretty good luck with BT devices, even ones that dont use standard GATTs

by Rebelgecko

7/29/2026 at 8:37:17 PM

Exactly.

I don't want a "smart" washer / dryer / fridge / toaster. I want a standard interface I can build my own system around, or use someone else's that they've already built.

by QuercusMax

7/29/2026 at 9:05:42 PM

I wish lock-in was as taboo as medieval Christian attitudes towards usury.

by Terr_

7/29/2026 at 9:26:25 PM

> Imprecisely yeet the stepper motor all the way left/right, toggling the target temp between “really really hot” or “really really cold”

> Option 2 certainly is the “jankier” of the two options, given that it relies on a second-order property (target temp) to power the unit on/off… but hey - whatever’s easier, right?

Isn't this basically how a thermostat works? I.e. there is a component that is binary on/off, and a thermometer is used to decide to switch on or off.

by asveikau

7/29/2026 at 8:52:32 PM

Maybe not as fun but my sun room window unit is controlled by an off the shelf $20 thermostat designed for Air Conditioners. It’s the LUX Win 100 and is date/time programmable and features a compressor lockout so it doesn’t burn out your window unit by short cycling.

If you have a favorite smart thermostat you could also wire up a receptacle with a contactor between it and a cord and a 24v AC transformer wired to the line side. This would make your window unit controllable just like a central air conditioner.

by Moto7451

7/29/2026 at 7:43:56 PM

It's insane to me that some new construction buildings still use PTACs. Having used too many of those, this was a deal-breaker last time I was in the market for an apartment. Such a New York thing, just like how you cannot have a balcony on the 2nd floor, or how you won't find those sink garbage disposal grinders in any kitchen. But cross the Hudson toward NJ, and my understanding is that they're common. It's a combination of hyper-local regulations and economic incentives that date from god-knows-when and make American cities very unique in their quirks.

by chem83

7/29/2026 at 8:46:17 PM

https://esphome.io/ would make the software side of this a 10 minute job

by vayun

7/29/2026 at 8:51:17 PM

This, I'm very surprised they didn't go with it.

by chpatrick

7/29/2026 at 9:39:16 PM

Oh, hey, I'm the author!

Happy to answer any questions :)

by daniel5151

7/29/2026 at 9:16:02 PM

I can't offer praise for controlling a mechanical thermostat with a poorly-implemented software thermostat.

If this was a remote control knob it might begin to make sense, but it isn't.

A NYC apartment with a 115V PTAC is by definition the size of a shoebox, is twisting a knob twice a day really that much of a burden?

by pudgywalsh

7/29/2026 at 7:17:29 PM

> The rest of this blog post is a walkthrough of a software engineer’s approach to home automation and building custom hardware, and let me tell you: both the final product, and the journey to get there, are hella jank.

IMHO it's not that bad? With the disclaimer that I'm also a software engineer who dabbles very very lightly with electronics and has no mechanical engineering expertise. But the overall approach of doing this by stepper motor seems quite defensible given the security deposit constraint. The only part that seems really janky to me is that it's not physically held in place that well as noted in this paragraph:

> Ultimately, the biggest issue is that binder clips and cardboard aren’t quite as robust of a mounting mechanism as I’d hoped they’d be… and over time, the stepper motor tends to “sag” a bit, resulting in a bit too much friction between the motor, the coupler, and the underlying knob, causing the mechanism to stall out until someone manually goes and reseats it…

Involving MQTT and HA can sometimes get frustrating too; having your AC not working properly if there's a problem on a Linux machine can suck. If this becomes a problem in practice, iirc ESPHome also has a thermostat component, and temperature sensors are really cheap and easy to wire in, so you could do it all on the microcontroller pretty easily in a low-code way. But if this part is working, no need to mess with it.

by scottlamb

7/29/2026 at 8:43:30 PM

That's what I did. Just an esp32 relay board with a tiny screen and a knob. Then I put more esp32 sensors in each room to get individual temps, with HA logic to select which room the thermostat pays attention to. If HA dies for some reason it falls back to a local control and I'm back to the same situation as before, a thermostat that only pays attention to the temperature in the hallway it's installed in. All the boards were flashed with ESPHome.

by barnas2

7/29/2026 at 8:23:13 PM

It does feel hella jank, but it's pretty obvious from the tone of the text that the author is fully aware of that. He went through every available option in order from reasonable to jank and this is the first one that worked.

There's nothing wrong with jank as long as it's not going to burn your house down the way some of his other rejected ideas would have.

by danudey

7/29/2026 at 9:09:14 PM

I'm curious: what other ideas did the author have, and why were they rejected? I can't find anything on their website.

by tentacleuno

7/29/2026 at 8:32:07 PM

I don't get how so many large buildings in NYC and Beijing (two cities that I've personally visited) use independent little AC units like the PTAC or minisplit types. A couple per apartment, peppered over the outer walls. Engineers intuition says surely a large central unit would be more efficient and effective.

Is it because of personal ownership reasons? Counterintuitive physics? Heat dissipation limitations on the roof?

Can someone with more knowledge clue me in?

by Liftyee

7/29/2026 at 8:34:01 PM

There are no air ducts to move air between the units. They are old brick buildings and retrofitting central air you might as well tear down and rebuild a lot of the time.

by trillic

7/29/2026 at 8:40:44 PM

Which of course means they should use heat pumps, since the copper lines don't need nearly as much room (I suppose you'd still have to put a drywall wall in front of one brick wall potentially). Even just putting a bunch of mini-splits on the roof (instead of individual window AC units) would be an improvement, seems like.

by blacksmith_tb

7/29/2026 at 8:52:44 PM

I had the option to buy a “central” unit or several mini splits for my apartment. I chose several mini splits. The main reason is that they can fail independently, so I’m not stuck in an apartment that is hot everywhere.

But I think the main reason is that in places without central AC, people tend to want to incrementally upgrade. For example, you might get a mini split just for your bedroom, because that’s the room you require the most comfort during the hot days. Then when you start getting used to the comfort of the AC in the bedroom, you’ll want one in the living room. And so on.

by drdexebtjl

7/29/2026 at 8:38:05 PM

OT: I'm looking for some way to control my AC via Infrared. I have a few pretty standard AC units with IR remotes. The ones with a display on it, that just transmit all the settings on the remote via IR on every button press.

Some device I can mount in proximity, that controls the AC, but preferably also has a temperature and humidity sensor included.

by andix

7/29/2026 at 8:52:42 PM

Some ACs have UART interfaces inside that can be fairly easily hooked up to an esp32.

You could also buy an IR transmitter module from AliExpress and add a temperature/humidity sensor chip on I2C like an SHT41.

by chpatrick

7/29/2026 at 8:45:42 PM

I use http://getmysa.com for this. they have their own app and scheduling, but i just automate mine via homeassistant

by mardef

7/29/2026 at 8:56:54 PM

This doesn't look like it can control the AC unit via infrared. How did you solve that part?

by andix

7/29/2026 at 9:20:40 PM

They have a version for mini-splits that is an ir blaster.

by mardef

7/29/2026 at 7:38:58 PM

I was in a similar situation with my apartment PTAC unit, but mine has thermostat terminals — I would not be surprised if this one does too. I was able to hook up an Ecobee thermostat, with the downside being that it's way more expensive than OP's solution.

by ethnt

7/29/2026 at 8:10:40 PM

30 years old PTAC has wired thermostat terminals. But I dolike OPs solution.

by newhotelowner

7/29/2026 at 9:14:02 PM

You need to 3D print a bracket. That's what will give you the last 10-20%.

by bmurphy1976

7/29/2026 at 7:44:17 PM

that's a fun project. i'd be a little concerned about the servos failing to fully switch the switches or placing wear on them, maybe a dangerous failure mode where it is switched into and left in an in-between state unattended that could lead to a fire hazard.

you can buy smart outlets with the correct connector, just look for 20A versions. (honeywell, at a minimum, sells one).

https://prod-edam.honeywell.com/content/dam/honeywell-edam/h...

by a-dub

7/29/2026 at 7:47:10 PM

The lack of feedback from the AC unit makes using a switched outlet potentially problematic. You really need to know the state of the compressor cycling before you go mucking with turning it on and off. (At least this was the case with the refrigeration compressors I am familiar with from my youth.) A current sensor could provide feedback but that goes beyond a regular smart switch.

by EvanAnderson

7/29/2026 at 8:50:46 PM

i don't think that's true. i still have a thinkeco ac modlet that coned sent me years ago as part of some kind of "make your ac smart" promotion.

if you turn those knobs to the off position while the compressor is running, does it actually go into some kind of orderly shutdown or does it abruptly cut power to the compressor?

by a-dub

7/29/2026 at 8:55:03 PM

The wiring diagram for this article seems to reflect it would be a hard shutdown. Most HVAC systems I have interacted with have zero problems with a sudden power loss. The only potential issue is bringing the compressor back up too quickly on the other side. You could easily control for this if you were switching the whole unit using software.

by bob1029

7/29/2026 at 8:03:58 PM

I have to say. Nice work. I spent years wanting to build something like this to integrate to these systems. I never did but have spent years thinking about this. So, nice work and really appreciate your motivation.

by ryeguy_24

7/29/2026 at 7:35:04 PM

Instead of attaching the motor bracket with a binder clip, consider sticking it down with some sort of removable adhesive?

3M command strips should be very strong/secure, while also allowing for adjustment and will detach without residue when the time comes.

by Reason077

7/29/2026 at 7:41:32 PM

I'd cut a block of wood to fit snuggly to the left of the knob, wedge it in place and screw the stepper in to that.

.....or just screw into the AC unit somewhere discrete and hope no one notices.

by itslennysfault

7/29/2026 at 9:11:00 PM

Just putty over it and get a slightly matching high-gloss or semi-gloss enamel and nobody will notice it. I've put tons of holes in things in rentals over the years and basically nobody will care as long as you restore it to like condition when you leave.

by throwway120385

7/29/2026 at 7:40:51 PM

Assuming running a dual hose inverter portable AC isn't against the lease agreement it would probably pay for itself based on the power usage. Pretty neat hack regardless.

by post_break

7/29/2026 at 8:53:02 PM

Portable ACs are generally less efficient than regular window ACs and PTAC units since the compressor is inside the room.

by arikrak

7/29/2026 at 9:21:23 PM

Yes, except for dual hose inverter ones.

by post_break

7/29/2026 at 9:23:30 PM

There are also portable split systems like Midea Portasplit.

by chpatrick

7/29/2026 at 8:45:02 PM

Another option would be to install a smart timer in the outlet. However, you need to ensure that the heat won't automatically go on when the device is turned off, and sometimes the outlets are non-standard formats.

by arikrak

7/29/2026 at 7:16:03 PM

Hey Siri, can I afford a home loan?

by effnorwood

7/29/2026 at 7:22:00 PM

You’ll need to unlock your iPhone for that.

by clickety_clack

7/29/2026 at 7:42:56 PM

Always a latch. That's key.

by effnorwood