Thermostat C-wire adaptor - no terminal on furnace?

Seeking guidance before purchasing the Wyze thermostat.

There are four wires run as such on both the thermostat and furnace ends:
Green wire to the connector with a green label ‘A’
BLUE wire to the connect with a YELLOW label ‘B’
White wire to the connector with a white lebel ‘C’
Red wire to the connector with a red label ‘D’
Conclusion 1: the blue wire is functioning as if it were a yellow wire. Anyone disagree?

Conclusion 2: The Wyze Thermostat C-wire adapter (CWA) will be required.
Assuming that is correct, the dillemma: there is no patch location on the furnace side of the CWA to connect the c-wire to. See left side of the second picture.

Where should the fifth wire of the CWA go on the furnace? (Bryan Evolution, about 12 yrs old).

Your current thermostat and furnace are wired up for communicating mode. The wyze is not a communicating thermostat. (None of the sub $300 smart thermostats by any manufacturer are)
You could rewire your furnace and thermostat, but you would lose any communicating features your current thermostat offers. If you’d like, I can walk you through how to do that,

I’d also recommend you check your condensate drain line to make sure it is clear, from the rust and water spotting in the pan of your air handler.


For those like me who have never heard of this, I found a rundown at

Apparently it’s a 4 wire system with an addressable serial port network.

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Thank you. I’ll investigate this communicating ’ design.

The article is very helpful. Thank you both!

I knew already that my system 8s efficient; My main motive was for remote monitoring and control. I don’t want it $300+ bad!


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