I have Lennox 78H2201 / 3AAT89A38A2 non-programmable thermostat and I wanted to replace with Honeywell RTH 7600D series programmable thermostat. Current wires setting is as follow: W ; Y ; G and R. When I connected wires to the new thermostat and did initial set up the fan was turning off and on all the time and the heat was not coming. I called Honeywell and they were not able to help me. When I put the old thermostat back on the wall, everything was just fine. Does anybody knows what is the issue? Thanks.