Lennox Thermostat Color/Letter Codes?


Old 06-12-08, 02:20 PM
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Question Lennox Thermostat Color/Letter Codes?

I just had a Lennox series HP18-211U-BP heat pump that was recently repaired (compressor failed). This unit was originally installed cica 1989. The other components were in very good shape so I opted for a repair instead of replacement. The HVAC contractor recommended that I install a digital thermostat to replace the Lennox P/N 36G6901 mercury switch thermostat which does not have a waiting period for intermittenened power interruptions (average 4 per week lasting 1 to 15 seconds each, average 7 seconds) which are frequent in my area. I obtained a Hunter 43855 programmable thermostat (to preserve the compressor and save energy) and the terminal designation do not match what is in the instruction manual. I looked online, and Lennox has been using non-standard Letter/Color codes for years. From what I have gatherered on the Internet the following is true for this particular setup, please correct me if I am wrong:

Function :: CTC -- Lennox Color
-------- :: ---------------------
Reversing valve energized in cooling) :: O -- Orange (R)
Control power :: Rc/R -- Red (V)
Fan relay :: G -- Green (F)
Compressor contactor :: Y1 -- Yellow (M)
Service light :: L -- Brown (L - not connected, but present)
Ambient sensor/thermistor :: ???? -- (A - unused, no wire available)
Electric heat - Aux/Emergency :: E -- White (Y)
Common RC :: C -- Blue (X)
:: ???? -- Black (E)


I just want to make sure I will be connecting the correct terminals with the proper color/letter codes.

I will be installing the CTC Model 43855 (By Hunter Fan similar to Model 44860)

The following connections are available for this thermostat:

Rh - Heating Transformer Power Supply (pre-jumpered to Rc/R)
Rc/R - Cooling Transformer Power Supply
C - 24VAC Common
Y1 - Cooling Stage 1
Y2 - Cooling Stage 2
W1 - Heating Stage 1
W2 - Heating Stage 2/Auxiliary Heat
W3 - Heating Stage 3
H - Humidity Control
G - Fan
E - Emergency Heat
O - Cool Mode Powered Reverse Valve
B - Heat Mode Powered Reverse Valve
L - System Monitor

The CTC thermostat manual can be found at: http://www.ntsupply.com/files/products/43885.pdf for more information.

Thanks in advance for any information that you may have for me.
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Old 06-14-08, 06:54 PM
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O -- Orange (R)
Rc/R -- Red (V)
G -- Green (F)
Y1 -- Yellow (M)
E -- White (Y)
C -- Blue (X)
So far good.

Is there W2 on the air handler? (or E or Aux?)

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