RTH3100C thermostat for an older Lennox heat pump

There's 100s of Lennox units and 1000s of tstats. What are the model numbers

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E Back up heat/ white wire
AUX Jumper to E
Y yellow wire / Cooling - compressor
G Indoor fan Green wire
O Reversing valve energised in cooling most units Orange wire
L unknown. consult your manual Leave open
R Main power Red wire
B Reversing valve energised in Heat Rheem units only.
C Common second leg of power Blue wire.

Compressor may not be coming on. Bad capacitor? Question is a bit vague.

Are you changing out thermostat? If so you must turn off power to your furnace or air handler. You should mark or write down each color and what terminal it was removed from. example= red from term r=green from term.=g yellow from y... Be careful, some thermostats are wired different according to type of system you have. Heat pumps are different than straight cools and the thermostats sometimes have setting or little switches. Honeywells have installer set up guides in package. Read it carefully

At tstat press options. Press installer setup. Yes, you are qualified. System settings, non heat pump. Gas/ oil heat. Save changes. That should do it with no wiring changes.

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Your original wiring configuration seems to indicate that you have an air conditioner (not heat pump) and either a gas or electric furnace. If this is the case you may need a different thermostat for your application.

Just remember what wires went to which terminal. Usually color coded, red =R, white = W, etc, Shouldn't be too hard. Let me know if you run into a problem.

Hi, If indeed you do have a heat pump, there wouldn't be any gas involved as a heat pump runs on freon with a reversing valve and heat strips for aux and emerg. heat. For gas electric operation thermostat terminals are rc to rh with factory jumper. Red wire to either.W to W for Heat, Y to Y for cooling G to G for Fan. If you have a blue, you wont need it unless this is a commercial stat useing a common for the Led lights on the stat. The unit will get its 24volts through R terminal in combination with y,w,and,g. Cant be a heat-pump if you have a gas furnace.Wrong t-stat. You need a gas /elect stat. And on a 24volt programmable t-stat, the batterys are used for the program only.If the batterys die, than you will loose the program on most residential stats. On commercial stats with the common in play, when batters die the stat defaults back to the factory settings.If you had a Lennox heat-pump stat on a gas/elect unit, you need to change it. Someone was using what they had on hand. Let me know if this has helped you.I will be here if you need me. Sincerely,
Shastalaker7

Bill ..You dont have a heat pump.This controller will not work for a conventional system. Get the right thermostat

if you have a newer t-stat your heat pump reversing valve is either o or b depending on the type of system you have