Hi
You could use ESP32 to build an IR sensor & add ESPHome to it.
Above link will help you check compatible Air conditioner brands.
Cheers
I second the Broadlink RM4 solution, if you don’t want to recable or purchase a whole new system or thermostat. I used to have my previous rented home AC controlled thorugh broadlink. It takes some time to train all codes, plus you don’t have a “current state” (you need to derive it from the actions your perform through HA), but otherwise very versatile.
Now i switched homes and my cheap landlord has this… https://manualzz.com/doc/63886127/watts-industries-ecolux-04.07.605-instructions good luck integrating that.
Sensibo also works well, although cloud.
Many Mitsubishi can be controlled by an esp directly without IR.
Many can be controlled by esphome via IR. ESPHome — ESPHome
And of course there is the list here to go through. Integrations - Home Assistant
Newer Mitsubishi equipped with WiFi module works through MELCloud integration.
There is, in mine opinion, just one annoying thing:
If I change something via remote, it takes around minute to see change in HA, and if something changed via HA remote never get update. But I can live with that.
Any midea branded AC?
EspHW described here:
Smart aircon tends to cost a pretty hefty premium over non-smart. I use the SmartIR HACS addon with a Broadlink RM4 Mini and it works very well. Obviously it doesn’t sync with the aircon’s remote, but I never use that any more anyway. There is a fairly large list of supported aircons here.
Wow Guy, thajs for the great Insights. A Lot to read. Will Post my solution, when implemented
I also use SmartIR with a broadlink, as the AC is a ‘dumb’ oldy…
But, as mentioned, no feedback, so if the AC misses an IR command, HA wouldn’t know about it 
So i prefer to use the EspHome module, easy and works flawless on my 2 other AC’s
I believe Sensibo stays in sync with the IR remote - in the sense that when you use the remote, Sensibo can read it as well as the AC reading it.
Mitsubishi via MEL cloud too. But in oposite direction, because my mitsubishi AC have ‘smart’ remote with display, it memorizes state of the AC and when is something changed via cloud, remote don’t see change. Not very important, but annoying.
Hast anyone experience with Samsung aircons with integrated WiFi?
Well, it is almost two years later now and I have currently the same question as Thomas stated in Sep. 2022. Now almost all new current available ACs are “smart” and can therefore be controlled by browser/web/app. But which of all those work well with HA? Any current recommendations for the German market? I do know that there is a well maintained list of working Integrations - but that does not list a personal recommendation. Using a remote ESPHome IR is an option but as I buy a new AC, I would prefer an API connection so I can read settings and stats as well.
Most midea branded AC’s can be fitted with an esphome module 
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What are your requirements for your A/C?
You can get a lot of branded Midea A/Cs in Germany, or if you are suited for that, in one of the EU markets, like Italy. There you can get even better prices.
I ordered my Olimpia Splendid via a german supplier, labeled with their name. Quite happy with it, and ESPHome is so much better than the provided Wifi-dongle from Midea. 
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You ask for the requirements. Well, I need to cool 3 rooms and therefore 1x3.5kw and 2x2.5 kw. They need to be low in noise but can be high in power consumption.
And the main requirement is - they need to be accessible in Home Assistant but please without the need to open them on the first day to modify the hardware.
Thanks for the link to the supported AC brands. However, it is not really my intension to buy brand new and then fit an esphome module inside the new AC as that will most likely end my warranty for the device on that first day.
You really, really need to inform yourself better, really. 
It’s not meant rude, but all your questions, and worries, are already answered quite often, not only here in this topic.
All this here works without interfering with the A/C unit. What you actually do, is preparing an USB dongle with ESPHome and put that in your unit. Depending on how exact you did the work with your dongle, it is something between putting a USB dongle into a USB port and not use the USB port, but the cables that are connecting it.
In the end, you’re doing exactly, what Midea (or whatever brand) does. You’re connecting a Wifi dongle with the unit.
There is no chance, you’d void the guarantee! Period!
Take a look at klimaworld(.)com and look for their own branded units.
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well well, that does sound like a valid idea. So that is a working solution for Midea and similar models. But what about the other big names on the market (Daikin, Mitsubishi, Panasonic …) do they work similar best with ESP32 or are there other solutions?
I know there’s the recently released Faikin module for Daikin.
Seems to work exactly like the Midea one does, in the sense that it’s just a dongle.
I don’t have any personal experience with it though (but have seen plenty of praise for it), so please do your own research before committing.
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