Replacing Lennox thermostat with NEST w/ pictures.

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Old 01-08-15, 03:53 PM
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Replacing Lennox thermostat with NEST w/ pictures.

Hello,

I have a Lennox Heat Pump (Model E16Q3-15-1P) using a Lennox mercury thermostat (Pt. No. 36G6901). I am looking for help in replacing the Lennox thermostat with the NEST from my previous home. The wires connected to the old thermostat are labeled R, V, F, M, L, A Y, X, and I am looking to convert them to the NEST labels. I have been able to find some posts on this forum where Houston204 broke down the wiring on a similar thermostat, but this one is just slightly different and I don't want to damage anything by assuming its the same.

Also, would I set the NEST to a specific single heat pump setting during setup?

Here is a pic of the old wiring
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Here is a picture of the wiring on the heat pump in case it is useful. On a side note, I noticed there are two sets of wires which makes me wonder where the other set goes. I have read about outdoor sensors but I am not sure if this applies to my unit. I just bought the house and still poking around. I should make this a separate thread and ask about that.
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The Furnace:
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And finally, the NEST:
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Thank you very much for taking the time to help me out. I really appreciate it.
 

Last edited by PJmax; 01-08-15 at 04:25 PM. Reason: cleaned up old t'stat pic
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Old 01-08-15, 04:14 PM
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Lennox = your wire = Nest = function
R = black = O/B = reversing valve
V = blue = Rc = 24 volt power
F = green = G = fan
M = red = Y = compressor
L = brown = tape off = fault light
A = white = tape off = thermistor
Y = orange = Aux = heat strip
X = yellow = C = 24 volt common

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Old 01-10-15, 12:53 PM
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Thank you!

Thank you for your help! I have the NEST installed and it is working properly. It appears that I have a Heat Pump and Auxiliary furnace which was news to me. Thanks again and keep up the good work!
 
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Old 01-10-15, 03:55 PM
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You are very welcome.

It took me a good while to make sense of this wire combination the first time that I came across it.

Someone had wired the heat pump with only Y and C for straight cooling and the homeowner removed the old stat and left it on a table along with a new stat for me to install.

These days smart phones and the internet is a great help for looking up diagrams.
 
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