Hello world. I have an Heat pump system with Natural gas back up furnace. It is using a Honeywell VisionPro IAQ thermostat and a Honeywell THM5421C equipment interface. I want to change to a NEST. Is there a wiring diagram for changing to this? The thermostat is only using the red, white and blue wires. The interface is using the red, white and blue wires hooked up to the 1,2,3 for the thermostat. Then there is C,R,RC,RH (The R, RC and RH are jumpered together) G,Y2,Y,W3-AUX2,W2-AUX,W-o/b. and an outside temp sensor for the heat pump. Thermostat is Red wire #1 on both, White wire is #2 on both, Blue wire is #3 on both. Inside the interface the furnace is wired to Red-R (that is jumped to the RC and RH, The HP Red is wired to the RC that is jumped to R, RC and RH. Brown-from both Furnace and HP are wired to the C. Green wire is on G from Furnace only. Yellow from both are wired to the Y. White from both are wired to the W2 AUX. Orange is wired to W O/B and goes to the HP. And the Black and Blue wires or wired to the outdoor Temp sensor. Please help....
