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drummerbear26 · Oct 24, 2007, 12:18 PM

I have a Lennox T90H110A137 Thermostat with the following terminal letters and wire colors:

G - blue wire
F - red wire
C - green wire
H - yellow wire
V - white wire

I want to install a Honeywell RTH6300B Thermostat. According to the RTH6300B Installation guide, it tells me to ignore wire color and only use the letter designations. The Installation guide has these letter designations:

G
W/OB
NOT USED
Y
R
Rc

It further says to use this chart if the labels do not match up:

C or X B - Do Not Connect
G or F
W or W1 H O B
Y or Y1 M
R or RH 4 V
Rc or R

Given that information, I have been able to match all but one wire up:
C=C - Do Not Connect
G=G
R=V
W=H

My question is, given that the Lennox has both G and F and the Installation Guide says G or F, am I suppose to hook both G and F to the G terminal or just the G wire to the G terminal?

Thanks in advance for your help

JasonHoldenCO · Jan 29, 2010, 05:38 PM

Did you ever figure this out? I have the same question.

cdquikmc · Mar 8, 2015, 07:19 PM

T-90H110A137
I know this post is old, but I just replaced this same unit successfully, so I figured I'd get some karma out of it and make it easy for anyone else looking.

Just to clarify, it's an ITT General Controls" thermostat, model T-90H110A137, 24 volts max, 0.8 AMP. I have a forced air heat and cooling system, which is also Lennox.

The main issue is the letters/labeling for each terminal does match "modern" standards. In addition, my wiring did match the colors either, so it was a combination of research and guesswork to get it to work. (Two disclosures: I'm not a professional as this is the first thermostat I've replaced and I changed this is March, so I didn't run the A/C for long.)

You can probably ignore the wire colors (in parentheses) but I included them just in case.
Old Lennox - (Wire color) - New Thermostat - [Function/what it does]
G - (Orange) - C - [Ground]
F - (Blue) - G - [Fan]
C - (White) - Y - [Cooling/Compressor]
H - (Green) - W - [Heat]
V - (Red) - RcRh - [Power/Voltage]

Looking at the old labeling, it makes a lot more sense since the letters actual mean something.