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Lennox Mercury to Nest


frankstallone's Avatar
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02-02-18, 08:32 AM   #1 (permalink)  
Lennox Mercury to Nest

Bought a home with a nice HVAC setup. Everything is fairly new expect, what looks like, the original Lennox mercury based thermostats. I wanted to replace them with Nest Thermostats and have, but I am not 100% sure I got it right. Let me tell you what I have, upload some photos, and let me know what you think. I confirmed with Nest that their thermostats will work with the setup I have. Also if you think there's a better place for me to post this question, feel free to reach out and let me know.

* HVAC Setup *

** Larger Unit **

LENNOX ELITE XP13-036-230 - 3 TON, UP TO 14.2 SEER / 8.5 HSPF, 208 / 230 VOLT, SINGLE PHASE, R410A HEAT PUMP.
CBX27UH-042, Upflow/Horizontal, Air Handler, Multi-Speed, 3.5 Ton, Elite Series

** Small Unit **

LENNOX ELITE XP13-024-230, Heat Pump, 13 SEER, 2 Ton, R-410A, Elite Series.
CBX27UH-030, Upflow/Horizontal, Air Handler, Multi-Speed, 2.5 Ton, Elite Series.

The Lennox thermostats have _no_ model numbers. The best I could find was a sticker with LR1620 on it but Google only finds Honeywell thermostats with that number. Calling Lennox was no help. They told me to call a Lennox Certified Dealer.

Both thermostats have the same wires run to them (this is at the furnace):

** @ Furnaces **

R - RED,
R - ORANGE,
G - GREEN,
C - BROWN,
Y1 - WHITE,
W1 - YELLOW,
O - BLUE

Then there is another wiring loom that goes to the same motherboard out to the heat pumps. For instance, R is jumped to the RED cable that goes outside.

** @ Nest thermostat **

Y1 - YELLOW,
G - GREEN,
OB - BLUE,
RC - RED,
W2 - WHITE
C - BROWN

** Photos of Thermostats **






** Photos of 2 Ton Units **







-- This last photo I am holding the loom going to the thermostat

** Photos of 3.5 Ton Units **



-- Only one photo because they're mostly the same, wiring wise.

 
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02-02-18, 09:05 AM   #2 (permalink)  
That stat is made by Honeywell.

 
frankstallone's Avatar
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02-02-18, 09:44 AM   #3 (permalink)  
Posted By: skaggsje That stat is made by Honeywell.
Cool. Still can't find a manual for it haha.

 
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02-02-18, 01:06 PM   #4 (permalink)  
Base number of Q672L gives a start. There are enough Lennox variants to drive you crazy. Shown in https://customer.honeywell.com/resou...0s/60-2485.pdf
In the end the thermostat doesn't matter so much as the air handler and compressor which you have already figured out.

Informative note listed for some of the Lennox:
Wiring differences (old=new):
V-VR=R, M=Y, Y=W2, F=G, R=O.

 
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02-02-18, 01:13 PM   #5 (permalink)  
I would be concerned that white and yellow are swapped. Need to check t the outside units to see what color connects to what there.

 
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02-02-18, 06:33 PM   #6 (permalink)  
Wow, that is a great start!! If I swap white and yellow, which is what the Nest support agents suggested as well, the heat no longer works. On Sunday I will take photos on the unit outside to confirm.

 
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02-03-18, 08:12 PM   #7 (permalink)  
I would not swap yellow and white as recommended by your tech support.
I can see why an installer might have connected the yellow wire to the Y terminal.
Yellow at the stat is electric heat strips with your system.

I see that you have a yellow wire and a white wire at the air handler W1 so the outdoor unit is wired with the more conventional white wire.





page 77 and 78 as seen on the page ( or pages 79 and 80 as seen at the top of the screen)

http://controlscentral.com/Portals/0...ference-HW.pdf


Last edited by Houston204; 02-03-18 at 10:46 PM.
 
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02-06-18, 09:38 AM   #8 (permalink)  
Hey guys! This is really great information. I was able to get outside and get the wiring from out there. Both units have the same wiring:

** 2 Ton XP13-024-230-03 **
** 3.5 Ton XP13-036-230-03 **

W1 - White
C - Black
R - Red
O - Blue
Y1 - Yellow

 
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02-06-18, 10:54 AM   #9 (permalink)  
ok. So you now know what's going on. When swapping in new thermostats it would be good to update the wiring in the air handlers so that only yellow is on Y1 and only white is on W1. That will make it easier the next time someone has to look at things.

 
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02-12-18, 05:25 AM   #10 (permalink)  
Thanks Astuff, that's a great suggestion. I haven't had a chance to test the air conditioning but it would appear everything is wired correctly.

 
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02-12-18, 05:28 AM   #11 (permalink)  
Also thanks to Houston204!

 
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