topic Re: Bryant / Carrier Evolution thermostats - some misleading answers in Nest Thermostats

Bryant / Carrier Evolution thermostats - some misleading answers

HansWSchulze — Wed, 22 Feb 2023 07:31:27 GMT

I have 2 sets of HVAC, one of which I started installing Google Learning Thermostat on, and searched far and wide for Nest related information on the Bryant / Carrier Evolution series. Could find nothing that says they were compatible, and some Google Nest experts claiming that they were NOT compatible.

After looking at the Bryant diagrams, and some photos, I found that this system, normally a 4-wire parallel interconnect (all units on a bus) which has 2 power wires, and a transmit and receive. I thought, that looks familiar, and then found that someone else had identified this as RS485 current loop bus, and that it might even support MODBUS (still not sure) and even found some source code out there.

Opening up the cabinet, I found the controller on the top had both 4-wire and legacy connection strips, with the same annotations as were on the Nest.

I had already hooked up the Nest at the thermostat end, and it woke up, wasn't feeling very energetic, and I found that it was possible that I needed a Common (C) wire, for which I borrowed a Blue wire from the remaining 4 wires at the Nest, and it was now happily chatting on the Wifi, downloading updates, tra la la.

I shut off the HVAC with the mandatory power switch on the wall next to it (why all states don't mandate this? Foolishness), but the cabinet cover had already done that for me, see black intrusion switch on the top. Seems that leaving this cabinet open could cause CO2 to leak from the HVAC, but I wasn't impressed by the door seal, far from gas tight, a bit more like wind tight.

My system was a bit more fangled, since it included an inline water sensor in the HVAC bathtub tray (what else do you call it?) which would cut off thermostat power if it got wet - it's in series to the thermostat ground (black), so you can follow the orange, red, black, green (off photo).

The RS485 is the 4-terminal green block on the right hand side. Removed one set of wires by elimination, and moved them to the old-style terminals at the top. It worked.

Now the question is, how to connect RS485 MODBUS to Nest?

The downstairs HVAC has 2 thermostats, 2 dampers, and AC/Gas heating (heat pump one day).

It seems there might be a way using Zigbee to RS485, working on researching that. Anyone else tried this yet? I mean, I could buy a board and hack the programming, or maybe there's enough smarts in the Nest device to speak MODBUS (a bit like the old AT MODEM commands, with some reliability stuff added). The point being, that there is so much information available in my HVAC, as others have posted, to measure efficiency and changes to insulation, that would warrent some sort of officially supported system. I would love to have variable fan speed control, and ownership of vacation temperatures by the basement thermostat. Also would love pre-emptive cooling, where, if the temperature outside is rising rapidly in the summer morning, that the AC starts removing the heat before it builds up in the mid-afternoon and requires grid battery backup to kick in. Or even to re-hookup the fresh air ventilation system which was disabled, that would kill the AC and open the outdoor air upstairs to cool the house around sunset if the temperature outside was lower than upstairs, which it is about half the time. Currently I have to manually open 2-4 sets of windows and/or skylights.

On the other hand, not much on photos is available on the web, possibly due to takedown requests? A handful of sites no longer own their domains. Lets see if this post lasts.

https://www.doityourself.com/forum/thermostatic-controls/636995-bryant-evolution-nest-thermostat.html shows a similar quest, and talks about using EcoBee4 as an option, but not sure how that hooks up to a smart HVAC.

Re: Bryant / Carrier Evolution thermostats - some misleading answers

Patrick_Caezza — Wed, 22 Feb 2023 07:41:35 GMT

All Nest thermostats only work with 24Vac systems. Period.

They will not work with any other types of interfaces. What you are describing is the hardware interface common to many HVAC systems with their own proprietary interface. Just because the hardware is the same doesn't mean the software used to communicate over the hardware is the same.

Your system has the 24Vac control terminals and you should just use those instead of the proprietary interface.

Re: Bryant / Carrier Evolution thermostats - some misleading answers

HansWSchulze — Wed, 22 Feb 2023 21:32:46 GMT

Um, that's the conversion from so called proprietary to legacy that I describe, since the last Platinum expert said it wasn't possible at all.

The MODBUS RS485 protocol predates Google.

Here is some details on the exact implementation, because there's enough "needs to be written exactly like this" that made MODBUS a not very well liked protocol. I wrote Javascript implementation on it over 20 years ago, that worked for a short list of devices.

https://github.com/nebulous/infinitude/wiki

Given the number of sense and assert pins on the Nest devices, I would have expected support for serial protocols might be a built-in capability. Even edge triggered bit banging would have worked. I did that 40 years ago.

Re: Bryant / Carrier Evolution thermostats - some misleading answers

Patrick_Caezza — Thu, 23 Feb 2023 04:54:38 GMT

It doesn't matter which predate which.

Like many other manufacturers, Nest only supports the 24Vac system to control the HVAC systems.

Re: Bryant / Carrier Evolution thermostats - some misleading answers

HansWSchulze — Thu, 23 Feb 2023 05:41:05 GMT

I don't know who you work for, but your courtesy leaves much to be desired.

I never argued the point about working with 24VAC. Period. There you go. I already know that, if you read my article/question.

If you want to do something positive, please add sources of useful information. Or correct some of the documentation. That's my way.

Re: Bryant / Carrier Evolution thermostats - some misleading answers

Jeff — Thu, 23 Feb 2023 19:18:30 GMT

Hey HansWSchulze,

We are always going to welcome new info and help when it comes to getting the Nest products working with a wider variety of applications and HVAC systems. I think what Patrick was getting at is that official support is more of a hardline issue. While the community might find workaround efforts, official documentation is never going to include those sorts of steps that veer outside the specs of the Nest Thermostats.

Personally, I admire the ingenuity of the community members, like yourself, that look for ways to extend how the products work. Officially, however, most of these ideas won't roll into official product support.

Thanks,
Jeff

Re: Bryant / Carrier Evolution thermostats - some misleading answers

Jhonleanmel — Mon, 27 Feb 2023 10:50:23 GMT

Hey folks,

We appreciate your help here, Jeff.
HansWSchulze, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

Re: Bryant / Carrier Evolution thermostats - some misleading answers

Markjosephp — Tue, 28 Feb 2023 15:04:27 GMT

Hello HansWSchulze,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours.

Regards,

Mark