Older Lennox Thermostat Color/Letter Codes - http://www.hvacmechanic.com/ Forums

Original message

Thurmont

76.100.242.164

"Older Lennox Thermostat Color/Letter Codes" , posted Thu 12 Jun 17:26

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.

Replies:

Houston204

98.196.66.53

"Re(1):Older Lennox Thermostat Color/Letter Co" , posted Thu 12 Jun 20:14

E = emergency heat. This is electric heat strips witout heatpump.

W2 is auxillary heat. Stage 2 heat running with heat pump.

It is not hard to remember this in the field.
R = Reversing valve (O)
V = Voltage (R)
F = Fan (G)
M = compressor Motor (Y)
X = common (C)
A = thermistor (T) unused with modern stats
L = service Light (L)
E = emergency heat (E)
Y = auxillarY heat (AUX/W2)

"Tip of the Day" Remember to remove power first.

Thurmont

76.100.242.164

"Re(2):Older Lennox Thermostat Color/Letter Co" , posted Sat 14 Jun 23:21

I installed the thermostat and tested it in all modes of operation at sunrise (so I could do the heating modes as well, normal, aux, and emergency) and works good including cooling. Once again, thanks for the info. Hopefully, this will help someone else as well who has the same issue too.

Thurmont

76.100.242.164

"Re(2):Older Lennox Thermostat Color/Letter Co" , posted Thu 12 Jun 21:57

Houston204,

Thank you a lot, I will install the thermostats tomorrow during daylight, this is the exact information that I was looking for. The idi0ts at Lennox couldn't help -- I called and e-mailed for their technical support.

R = Reversing valve (O) - Orange
V = Voltage (Rc/R) - Red
F = Fan (G) - Green
M = compressor Motor (Y1) - Yellow
Y = auxillarY heat (AUX/W2) - White
E = Emergency heat (E) - Black
X = common (C) - Blue
L = service Light (L) - Brown

A = Thermistor (T) unused with modern stats

Thanks, & Have a Great Day!

Houston204

98.196.66.53

"Re(3):Older Lennox Thermostat Color/Letter Co" , posted Thu 12 Jun 22:14

I spent hours trying to figure this information out the first time I came across this. Someone had replaced the Lennox heatpump outside with a Goodman and butchered the wiring. They wired the new heat pump outside with 2 wires.

I noted my findings on my iPaq.

"Tip of the Day" Remember to remove power first.