Replacing lennox thermostat, with diagram
G-green
O-orange
RH & RC- red, same wire spliced
W-white
Y-yellow

Replacing with Honeywell T8400R model, diagram
G-green
C-blue
R-red
W1-yellow
O-white

Can't get system to blow cold air. What went wron?

Are you sure about the model number, could it be rth8400r ? Most come with a CD rom set of instructions and those that don't have a paper manual. I don't have yours but try switching the white and yellow.

You need 4 things to get cold air. If the system isn't doing anything, you need to identify where the thermostat gets it power, and make sure it is. Once the thermostat has power, it must switch it to 3 places, the air handler relay, the outside compressor relay, and the reversing valves must have the proper signal.

Go to the sticky at the top of the Heating and Air conditioning forum to see how heat pumps work and what the different thermostat wires do. If you don't have the manual for the thermostat, there is another sticky in Electrical and Lighting on finding thermostat manuals. Some of the answers you need must come from Honeywell. Their tech service has baffled many here.