Wiring – How to install a Honeywell RTH65800WF Wifi thermostat

thermostatthermostat-c-wirewiring

I am having some difficulty figuring out the correct wiring for my new wifi thermostat. Before I bring out the A/C technician, I was wondering if anyone here might be able to help? Searched other threads and did not see one that applied to my situation…

It is a Honeywell RTH65800WF, watched all of their videos and spoke with their support department and still no luck, so here it goes:

Existing Thermostat Terminals:

  • G – Green Wire,
  • Y – Blue Wire (previous owner wrote a B next to Y label),
  • W – White Wire,
  • RH – Red Wire (with jumper to RC terminal) (previous owner appears to have highlighted the R),
  • B – Empty,
  • O – Empty,
  • RC – Jumper to RH terminal

Existing AHU Terminals:

  • C – Blue Wire,
  • R – Red Wire,
  • G – Green Wire,
  • Y/Y2 – Yellow and Gray Wires (not sure where these lead to , but I think to outside unit),
  • O – Empty,
  • W1 – White Wire,
  • W2 – Empty,
  • Y1 – Empty

New Thermostat Terminals (need to connect to):
C, G, Y, W, R

So it appears the C terminal at the Air handling unit (AHU) block is currently connected to the Y terminal at the existing thermostat? Is that possible?

I will attempt to include photos of the AHU and Existing Thermostat terminal blocks:

AHU:

enter image description here

Ex. Thermostat

enter image description here

Best Answer

I've labeled your photo, which should help you understand what's going on.

enter image description here

What you describe as a "blue" wire at the thermostat, you describe as "gray" at the air handler. I can't be sure, since I'm not there, but I think they are one in the same.

If you want to install a fancy new WiFi thermostat, you're going to have to pull an additional wire from the air handler to the thermostat. Once you have that, you'll connect one end to the C terminal of the air handler, and the other end to the C terminal of the thermostat.

Related Topic