Old Lennox Mercury thermostat to Nest conversion help


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Old 09-10-14, 01:31 PM
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Old Lennox Mercury thermostat to Nest conversion help

Hi all. Iím a new homeowner of a 1970ís-ish house. I am looking to replace an original (I think) Lennox Legend mercury thermostat, with a new Nest thermostat. As you may have guessed, the letters and color codes do not match! I'm hoping that someone can help me with the conversion. Here is what I have noted for the old Lennox thermostat:

Model#: 66F0001 (on sub-base)
65F9901 (on base)

Letter:Wire Color

VR:Red
V:Bare
X:White
M:White
L:Empty
F:Blue
R:Green
M2:Green
E:Empty
Y:Blue & Red (two wires attached here)
A:Red

On the Nest, the letters offered are

Y1
Y2
G
OB
Rc
W1
W2 (aux)
C
*
RH

Would any one be able to help me cross-reference these letters? Thanks in advance. Iíve enclosed a pic as well.
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JP
 
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Old 09-10-14, 05:38 PM
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Welcome to the forums.

This is going to be a little tricky. Normally an 8 wire cable would be run..... not two 4 wire cables with the same exact colors.

What kind of system do you have there ?
Heatpump ?
Electric reheats ?
Gas reheat ?
Gas furnace with regular A/C ?
 
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Old 09-10-14, 05:54 PM
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Old = New

VR:Red = R
V:Bare
X:White = C
M:White = Y
L:Empty
F:Blue = G
R:Green = O
M2:Green = Y2
E:Empty
Y:Blue & Red (two wires attached here) = Aux
A:Red = Tape off

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PJ you are welcome to copy this pic and use it when needed.
 
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Old 09-10-14, 08:55 PM
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Thanks for your response PJmax, I believe Houston204 has replied as well, but for what it's worth...I believe it's regular central A/C & heat.
 
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Old 09-10-14, 08:58 PM
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Thanks Houston204 - one more question..

Thanks Houston204 for your reply. I appreciate it. Does "R" from VR:Red=R correspond to RC or RH on the Nest?

Thanks again. JP
 
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Old 09-10-14, 08:59 PM
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So be sure to ID the wires since you have two sets of the same color.


Rh should be fine.
 
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Old 09-10-14, 09:43 PM
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That is a heat pump thermostat with a 2 stage outdoor unit and auxiliary heat.

Yep, connect the old VR to the new RH
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Old 09-11-14, 06:47 AM
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Thank you both. It's great to have this type of forum for these handyman jobs!

JP
 
 

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