Smart Thermostat Compatibility

Captured from ChatGPT on 8/17/2026

User

Can I replace this thermostat with a smart one that is connected to the Wi-Fi?

ChatGPT

Yes — but not with a normal Nest/Ecobee-style thermostat directly.

From the photo, this appears to be a Mitsubishi Electric PAR-21MAA wired MA controller. Mitsubishi documents it as a non-polarized 2-wire MA remote controller, meaning those wires carry Mitsubishi's control communication rather than conventional 24-V thermostat signals. Mitsubishi Electric Document Library+1

The best approach is usually to keep or replace the wall controller and add a Mitsubishi-compatible Wi-Fi interface to the indoor AC unit. Mitsubishi offers Wi-Fi interfaces such as MAC-567IF / MAC-587IF, which provide phone/tablet control through MELCloud for compatible M Series, Mr Slim, City Multi and other systems. Living Environment Systems

Alternatively, depending on your exact indoor-unit model, there may be a newer Mitsubishi controller or a thermostat interface that lets you use a more modern smart thermostat. Compatibility depends on the indoor AC unit, not just this controller.

What I need to identify the exact replacement

Open the lower flap on this controller and send me a photo of what's underneath, and ideally send me a photo of the model-number label on the indoor AC unit (for example, something beginning PEA-, PEAD-, PCA-, PLFY-, etc.).

Once I have that model number, I can tell you specifically:

  • whether you can completely remove this controller,
  • which Wi-Fi/smart thermostat is compatible,
  • whether you can use something like Google Nest,
  • or whether Mitsubishi's own Wi-Fi interface is the better solution,
  • and how it would be wired.

Don't buy a standard Wi-Fi thermostat yet—it generally cannot simply be connected to the two wires currently going into this PAR-21MAA. Mitsubishi Electric

User

IMG_C3FD67E3-647D-4577-ACC7-0F08F5FE1773.jpeg

ChatGPT

Yes — this confirms it clearly: your controller is a Mitsubishi Electric PAR-21MAA.

The important part is that this is an MA-bus controller, not a conventional 24-V thermostat. Mitsubishi lists the PAR-21MAA for City Multi and Mr. Slim, and its current replacement is the PAR-41MAAM. Mitsubishi Electric Australia+1

So you cannot simply replace it with a Nest, Ecobee, or generic Tuya Wi-Fi thermostat using the existing two wires.

You have a few upgrade paths

1. Add Wi-Fi to the existing Mitsubishi system — probably the best option.

A Mitsubishi Wi-Fi module can potentially be installed at the indoor AC unit, giving you app control while the PAR-21MAA remains functional. The exact Wi-Fi interface varies by indoor-unit model; for example, some compatible Mitsubishi systems use MAC-series Wi-Fi interfaces. device.report

This can give you remote:

  • On/off
  • Temperature
  • Cooling/heating mode
  • Fan control
  • Scheduling

2. Replace this old-looking controller with a modern Mitsubishi controller.

The current replacement for your PAR-21MAA is the PAR-41MAAM. Mitsubishi Electric Australia Mitsubishi also has touch-screen MA controllers such as the PAR-CT01MAA, although compatibility needs to be checked against the indoor unit. Logicool

That could give you a much more modern wall interface, while Wi-Fi could potentially be handled separately.

3. Use Nest/Ecobee through an interface.

This is sometimes possible, but you'd need a Mitsubishi-to-conventional-thermostat interface appropriate for your particular indoor unit. I wouldn't choose this route unless you specifically want Nest/HomeKit/Google Home integration, because you can lose some Mitsubishi-specific functionality.

One more photo will tell us exactly what you can install

The controller model unfortunately doesn't tell us which indoor unit you have. PAR-21MAA was used across many different Mitsubishi systems.

Find the Mitsubishi indoor unit—if your AC is ducted, it may be above the ceiling—and photograph its label. I'm looking for something like:

Model: PEAD-..., PEA-..., PLFY-..., PEFY-..., PCA-..., etc.

Once you send me that label, I can check the exact model and tell you which Wi-Fi module works, whether a modern touchscreen can replace this controller, and whether we can get it into Apple Home/Google Home/Alexa.

User

It is a ducted unit

ChatGPT

Yes — that actually makes the setup clearer.

Your PAR-21MAA is very commonly used with Mitsubishi ducted/ceiling-concealed systems, including Mr. Slim/P-Series and City Multi systems. Mitsubishi confirms that the PAR-21MAA is an older controller whose current wired replacement is the PAR-41MAA. Mitsubishi Electric Australia+1

For a ducted system, I would not replace the wall thermostat with a generic Wi-Fi thermostat. Instead, the cleaner solution is usually:

Ducted indoor unit → Mitsubishi Wi-Fi interface → Wi-Fi router → phone/app

The Wi-Fi module connects directly to the control board inside the concealed ducted indoor unit, rather than to the two wires behind your PAR-21MAA. Mitsubishi specifically says these Wi-Fi interfaces can be retrofitted to compatible existing systems. Mitsubishi Electric Australia

The important question now is how old your ducted unit is. For example, Mitsubishi's MAC-568IF-E officially supports compatible M-Series, P-Series and City Multi indoor units manufactured after January 2015. Mitsubishi Electric Australia Your PAR-21MAA is old enough that your AC could predate that, so I don't want to tell you to buy a particular adapter until we know the indoor-unit model.

Finding the model number

Since yours is ducted, you probably won't see the indoor unit normally. Look for an access panel in the ceiling, often near the return-air grille. The Mitsubishi unit above the ceiling should have a label containing something such as:

PEA-RP... PEAD-RP... PEAD-M... PEFY-P... SEZ-...

You don't necessarily have to access it yourself. The outdoor condenser's model-number label would also be useful. Take a photo of that label and send it to me.

Once I have the model, I can check the exact compatibility and tell you whether you can do something like a modern Mitsubishi touchscreen + Wi-Fi, keep the PAR-21MAA and simply add Wi-Fi, or use a third-party smart-home solution. Mitsubishi also offers the PAR-CT01MAA full-colour touchscreen for compatible ducted systems. Mitsubishi Electric Australia

If your main objective is Apple Home/HomeKit, tell me that too, because I'd approach the upgrade differently than if you simply want to control the AC from your phone.