Bryant Evolution with Nest Thermostat


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Old 06-17-22, 09:45 AM
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Bryant Evolution with Nest Thermostat

Hi, I have a Bryant Evolution 95s that I put a Nest thermostat on back in January. At the time, I rewired at the furnace from the ABCD terminals to the standard labelled terminals. The first 2 pics show the original wiring at the furnace and the thermostat. (Note that there is a 5-wire line from the thermostat to within a few feet of the furnace [blue is not used]. From there, it is a 4-wire line the rest of the way, and the yellow from the 5-wire is spliced to the blue in the 4-wire. This is why the blue wire is in the yellow "B" port in the furnace.) At this time, the AC red wire is in COM/24V, and the AC white wire is in Y/Y2.

The next 2 pics show the way I rewired it in January. I put the green wire in G, the white wire in W/W1, the blue wire (which is really yellow) in Y/Y2, and the red wire in R. I left the AC wires alone. I then finished setting up the Nest thermostat, and it worked fine all winter.

When I went to change the mode to cooling several weeks ago, I realized that the Nest was not seeing the AC. My only two options were Heat or Off.

Since I know that Nest's sometimes freak out without a common wire, I decided to add one... The next 2 pics show that change... At the thermostat end, I plugged in the unused blue wire into the C port. On the furnace end, I removed the 4-wire line, and replaced it with a new piece of 5-wire line. So now the yellow wire really is the yellow wire and it is still in the Y/Y2 port. The newly added blue wire is now in the COM/24V port. Aaaand, nothing changed. I can still heat and I can still turn it off, but no cooling option is showing on the Nest or in the app.

Any advice???

One further thing... The last 2 pics I just took last night of the inside of the AC unit. If I am following the lines correctly, it seems to me that the RED wire coming into the furnace from the AC is connected to a brown wire in the AC, plugged into the doohickey, and possibly coming from there as a yellow line into the unit. And the WHITE wire coming into the furnace from the AC is connected to a blue wire in the AC, plugged into the doohickey, and possibly coming from there as a red line into the conduit and back into the house.

This makes me think that the connections of these AC wires in the furnace are actually backwards. The red one is actually the yellow in the AC, but is in the COM/24V in the furnace, and the white one is actually the red in the AC, but is in the Y/Y2 in the furnace. (I may be wrong about this.)

So, I hope this is not too confusing for you! I really tried to be as clear as possible. Unfortunately, I am very confused about why I can't get the Nest to see the AC. Any help you can provide is very, very much appreciated!!! I am a mechanical engineer, so I really ought to be able to handle this...

Thank you,
Marc

original wiring at the furnace

original wiring at the thermostst

rewired for Nest in January at the furnace

rewired for Nest at the thermostat

added blue common wire & changed yellow wire to actually be yellow

added blue common wire

ac wiring

ac wiring
 
  #2  
Old 06-17-22, 08:05 PM
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Welcome to the forums.

It's like trying to stump the pro...

Firstly.... there are two wires connecting the outside condenser to the furnace board.
Since it's AC there is no polarity.

You basically converted from communicating to legacy/standard wiring.
There may be DIP switches that need to be changed but your nest should be operating correctly.
The current wiring looks ok.
If the nest is not acting correctly it may be because it hasn't seen a wire change and is still programmed for the original wiring. You need to reboot the nest so that it sees the new wiring connections. Basically start from scratch in setup.
 
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Old 06-20-22, 06:09 AM
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Thank you, Pete! You were exactly right...... All I had to do was delete the Nest from my home, and then re-install it. As soon as I did that, the Nest was seeing the AC, and all is working properly.

So simple, and yet I hadn't thought of doing that. Thanks again... You saved the day!!!

Marc
 
 

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