# Forum Home Renovation Heating & Cooling  NEST with Mitsubishi AC

## tricky4000

Hi everyone, Has anyone had any luck replacing the Mitsubishi Controller PAR-21MAA?  With a NEST controller (below)?  https://nest.com/thermostat/life-with-nest-thermostat/  If anyone has any ideas I would love to spend the $249 and upgrade my AC system at home. Tricks

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## OBBob

Seems to be an American site, are you sure that's the Australian price?

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## tricky4000

Hey OBBob,
Correct, this is American but extremely popular.  You'll have to convert the american dollar price.  Probably around AUD$350.
Tricks

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## OBBob

Ah ... fair enough. Interesting product ... these gadgets always tempt me and then I think about how much time I'd spend fiddling and trying to get it just to do what the original controller did! LOL.

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## FrodoOne

It is American - so the price will be in USD - plus postage. 
Assuming that the existing controller is operating on Extra Low Voltage (NOT 230 V) the NEST controller should work.
Go to https://nest.com/thermostat/install-and-explore/  click on "See if NEST will work in your home" and follow the directions.
(Also, watch the installation video.) 
Surprise! It can be set to Celcius (See https://nest.com/support/article/Doe...ure-in-Celsius)

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## tricky4000

@FrodoOne,
Oh yeah, already did that, the Mitso controller only has two wires, A&B.  Nest support don't know if this will communicate with my AC unit.  Maybe someone has seen them working together?

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## FrodoOne

> @FrodoOne,
> Oh yeah, already did that, the Mitso controller only has two wires, A&B.  Nest support don't know if this will communicate with my AC unit.  Maybe someone has seen them working together?

   Earlier, I did not look at the Mitsubishi instruction/installation manuals. I had assumed that this device would use the "Standard" multi-wire configuration as used (in general) by US manufacturers of heating, cooling and associated "control" equipment.
I now see that this is not so. 
Since the Mitsubishi control (presumably) associated with a Mitsubishi Air Conditioner has only two wires connecting it to the A/C, it seems obvious that these supply the "power" to the control and also act as the "channel" over which coded signals are sent to control the A/C.
Because of this, I am now certain that the NEST controller cannot be made to work with the A/C unit - without somebody, somewhere coming up with a suitable "interface" between the "Standard (US) system" and the Mitsubishi (propitiatory) system. 
Using the terms "PAR-21MAA", "NEST" and "Interface" I have not been able to find any such device when searching. 
I wish you luck, but . . . ! . !

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## Brian7886

the Mitsubishi remote will be a 12v set up, transformer would be in the indoor PCB, which is mains power supplied (230vAC). Doubt it will be able to talk to the control board effectively, and will probably throw fault codes due to mis communication.  
Another thing to consider if there is a fair chance the Mitsi controller houses a thermistor, which measures the room temp, and sends that data back to the PCB to allow for capacity control and air flow control.  
Im sure it CAN be done, but would be a lot of fiddling around, and if the device itself is $350, youll pay for a few hours labour for someone to come and work it out, which you will be charged for whether it works or not. So you could end up spending $700-$800 for something that does not work.  
Contact your local Mitsbushi agent, a lot of the time there is a modern controller that will be brand specific that is able to be adapted, could be touch screen, or a neater backlit control from the existing.  
Most brands i deal with have 2 or 3 controller options, the basic one being close to what you have pictured up there

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## tricky4000

Hey Brian7886, 
Just to confirm my controller simply has two wires and that is all.  No extra power supply.  It simply connects to the indoor unit.  It is powered via the single pair communications cable.  Yes, my controller does have an on-board thermostat.  It also adjusts the air flow, with a low and high setting (2 speed).  It also has the timer controls as well as function control (heat, cool, fan dry, etc).

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## woodbe

Have you tried this?:  https://nest.com/widget/compatibility/

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## woodbe

Also, look here:  http://www.mitsubishicomfort.com/sit...terface_pr.pdf

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