Hi All, I've been reading all posts that are similar to my units and questions but I've still got a few questions.

I believe I have the upstairs wiring down for a 3d gen nest.

The downstairs is where I could use a little help.

Downstairs is powered by gas Trane XV80 for heat and XL16i (need to double check #) for AC.

Thermostat is TCONT802AS32DAA

Based on the current wiring & features, would the nest make sense for this setup?

 

Yes, as long as you don’t get the stripped down Nest E. You can install a Nest thermostat on your 2 heat / 2 cool system.

 

Thanks, Houston! Would this be correct for downstairs wiring?

7-Wire TRANE Wiring: -------------> NEST
Red = 24v hot ----------------------> Rh
Black = Heating 2nd stage --------> cap off *
White = Heating 1st stage --------> W2/AUX
Yellow = Cooling -------------------> Y1
Green = Fan ------------------------> G
Orange = SOV ---------------------> O/B (program for O)
Blue = 24V Neutral ----------------> C

With that, I do think I've confused myself with all the photos. The upstairs 8 wire thermostat was where I was scratching my head. It's an xl16i too but with heat pump. Unfortunately, I don't have a photo of the board at the handler. Same thermostat .Here's wiring...

 

Brown on Y2
Black to * terminal and configure for emergency heat.

Is this also a dual fuel application? ( Propane furnace paired with a heat pump)

 

 

Second floor all electric heat pump system.

Red - Rh
Green - G
Yellow - Y1
Brown Y2
Orange - O/B
Blue - C
White - W2/AUX
Black - * (programmed for E heat)

 

Thanks for the replies!

Here's the upstairs air handler. Is it worth taking the cover off to see where the wires are placed before I install the nest?

Going to read the pro guide before I install.

 

 

Red = 24v hot ----------------------> Rh
Black = Heating 2nd stage --------> * (program for E heat)
White = Heating 1st stage --------> W2/AUX
Yellow = Cooling -------------------> Y1
Brown = Cooling- 2nd stage ------> Y2
Green = Fan ------------------------> G
Orange = SOV ---------------------> O/B (program for O)
Blue = 24V common ----------------> C

When you set up the nest..... you must tell it dual fuel in programming.

 

Thanks for the reply, Pete. I don't have an orange at the downstairs tstat but there is one at the handler. Would I just ignore orange in your list or does that change things? Thanks!

 

Now I'm confused. I knew discussing two systems in one thread would be confusing.
I thought the board in the first picture was the downstairs unit.

Hmmmm..... is that correct.... an orange jumper from R to O ?
That's not a usual connection.

 

PJ that is normal when a Trane or American Standard furnace or air handler is matched with a two step scroll compressor.

What usually throws people off is that stat Y1 doesn't connect to furnace YLo. Stat Y1 connects to furnace Y2.

Stat Y2 connects to furnace BK.

The BK jumper to R (dip switch) and jumper between O and R must also be addressed at the furnace.

This is to address the fact that Y1 is 50% of Y2 airflow with Trane. They have a two compressor condenser that is indeed 50% capacity with Y1. I hat is when the Y1 terminal is used.

I prefer the Trane furnace that had a Marquis. It allows you to configure for two step scroll without losing the BK for dehumdification feature.

 

Thanks for the info partner.

 

https://www.doityourself.com/forum/t...-needed-2.html


You are very welcome.

Post 7 has a diagram .

 

 

 

The changes at the furnace should already have been made.
You should be able to connect the new stat like the old stat was connected.

 

 

It looks looks the dip switch settings are ...

S3 = Off. Off, Off, On
S4 = On, Off, Off, On

What about S5 ?
Is S5 switch 2 Off? It needs to be off.

I see that thee R to O jumper has been installed as required.

What is the model number of the downstairs furnace?
What is the model number of the downstairs outdoor unit?

We want 350CFM per ton (if you are in a humid climate) but we need the tonnage of the outdoor unit and of the furnace.

 

 

I see that blower ramping is not on.
Counting from left to right 5 and 6 should be On for ramping. (AKA S3 -1 & 2)

1-Off
2-Off
3-Off
4-On
5-On
6-On
7-Off
8-On

S5-2 needs to be Off

 

The dip switch information is on the blower door. I took that picture with an old camera and it is difficult to read.

It would be great if you could post a better picture of the dip switch chart on your blower door.

 

Hey Houston,
Here are a couple pics of the blower door diagram. I split it in two for easier reading. Let me know if it's not clear.

I'm going back down to the basement to look over the switches again. I haven't changed anything since we moved in last fall.

 

Here's a close up of the chart. It must have dropped off in my original reply.

 

From your pictures I can tell you that S3...
1-off
2-off


S5-2 = off

 

Thanks, Houston! I'm not sure I comletely understand the settings for S5-2. Does it need to be switched off because of the installed jumper?

I wrote out my notes on the nest wiring but I left them at home. I think the only changes to the nest wiring were blue C and red to Rh? Does that sound right? I'll confirm later today.

 

S5-2 needs to be off because we have a 2 step scroll compressor connected to it.

When you turn the switch off it will open an internal jumper between BK and R.

The thermostat Y2 will then control the BK terminal.

 

I think I've got it now. I guess it's been operating less efficiently than it could be. Thanks!

Here are my nest notes:

Yellow - Y1
Brown - Y2
Green - G
White - W1
Black W2
Blue - C
Red - RH

Should I set up anything special in the nest other than dual fuel?

 

I'm sorry but you don't have a dual fuel setup.
A 4TTX condenser is not a heat pump.
Trane puts a W early in the model number with heat pumps. Like 4TW...

You have a 2 heat / 2 cool conventional system with a 2 step scroll compressor.

The use of the O terminal may have caused some confusion early in this thread but you don't have a dual fuel system .

A dual fuel system is usually a heat pump paired with a gas furnace.

 

Thanks for the clarification, Houston. I probably should have started two separate threads for the different systems .

 

Quick question...would there be any reason to enter the pro set up when I install the nest? It seems like the downstairs is a standard set up knowing what i know now.

 

While the Pro entrance would not be of much use , I like the test option.
I think it is around two clicks to the right of that.

I energize stage one cooling and count the flashes at the furnace LED.
I also measure the temperature in stream and leaving the evaporator coil.

I then energize stage two cooling at the thermostat and again count the flashes at the furnace and measure the temperature entering and leaving the evaporator coil.

Each flash at the furnace is 100 CFM, and we want 18 to 21 degrees delta T in both low speed and high speed.