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Compatibility wiring

WAS6868
Community Member

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....

3 REPLIES 3

zoeuvre
Community Specialist
Community Specialist

Hi WAS6868, 

 

Thanks for reaching out to us, and I appreciate your interest towards with our Nest Thermostat.

 

I see that your thermostat wires are most likely using a relay to convert its compatibility to your heat pump. Therfore, your system is proprietary. Proprietary systems aren’t compatible with Google Nest Thermostats. However, some proprietary systems can be rewired by a pro installer to be compatible.

 

Let us know if you have any other questions. We're happy to help. 

 

Best, 
Zoe.

zoeuvre
Community Specialist
Community Specialist

Hello there, 

 

I wanted to check and see if you managed to see the information I shared. Please let me know if you have any questions from here. I would be happy to assist and make sure you are good to go.
 

Thanks,

Zoe

zoeuvre
Community Specialist
Community Specialist

Hello WAS6868, 
 

We haven't heard from you in a while, so we'll be locking this thread if there is no update within 24 hours. If you run into any more issues in the future, please feel free to create a new thread.

 

Regards, 
Zoe