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Have a Lennox G8-I37 Furnace with no c wire

LloydL
Community Member

I have a G8-I37 Lennox Furnace and it has R, W, G.   have attempted to use G for my C and system failure, and also tried to use W for C and also received failure.  Looked at the nest power connector but the wiring diagram does not match what I have.  

I have tried to load a few photos of the wiring but it goes:

R is attached to yellow     Yellow it attached to transformer

G is attached to blue        Blue is attached to Auto main control valve

W is attached to second blue     this is attached to the fan and limit control

 

I would up load pictures but do not have permission

 

 

 
3 REPLIES 3

Markjosephp
Community Specialist
Community Specialist

Hello LloydL,

 

I understand you're facing some challenges with wiring your G8-I37 Lennox furnace to a Nest Thermostat, and it seems like the conventional wiring doesn't align with the Nest's configuration.

From your description:

  • R is attached to yellow, and yellow is attached to the transformer.
  • G is attached to blue, and blue is attached to the Auto main control valve.
  • W is attached to a second blue, and this is connected to the fan and limit control.

 

It appears that the existing wiring does not match the standard color-coding used in most HVAC systems. It's crucial to correctly identify the function of each wire to ensure compatibility with the Nest Thermostat. Which type of Nest Thermostat do you have? Make sure to update its software before installing the Nest Power Connector. Also, to insert an image in a post:

 

  1. Ensure that you are logged in to your Community profile.
  2. Reply to this post.
  3. Click Insert Image. (camera icon)
  4. Choose an image source location.
  5. Follow the on-screen instructions.

 

I look forward to your response.

Regards,
Mark

I have a gen 1 and yes everything is up to date.  This unit was put in in the late 70's or early 80's when I ran the product number it was made 1977.  

Markjosephp
Community Specialist
Community Specialist

Hey there,

Thanks for the details. Can you post a picture here of your old thermostat's wiring setup? The instruction is in the above post.

Keep me posted.

Best,
Mark