Wyze Thermostat control board only has red R, G, W

After waiting months to attempt to install the Wyze Thermostat (because after reading reviews I did not want to be without heat during the cold months), I discovered the control board in my furnace only has a R, G, W connector. There is nowhere to connect the yellow or blue. The current programmable thermostat has a G, Y, W, RH and a jumper between RH and RC. The R, G, W from the thermostat all go to the respective connectors on the Controller Board. There is a Blue wire that is not connected to the Thermostat and not connected to anything on the Board end. The yellow from the thermostat is connected directly to a red wire (2 wire cable in brown sheathing) that goes to the Central Air Compressor outside. The other wire coming from the Central Air Compressor is white and is connected to a green wire with a wire tie. This green wire then connects to a bare copper and green wire with a wire tie. The other green wire from this connected appears to be connected with a blue wire to the frame of the blower as a ground.

I am not really sure how to connect the yellow wire coming from the thermostat and if I should do anything with the white wire coming back from the Central Air compressor.

I am thinking that maybe the adapter would be used and the yellow wire would go to the adapter and then the red wire going to the Central Air would be connected to Y wire from the adapter. I’m not sure what to do with the c wire coming from the adapter. I am thinking the R, G, W wires would go to the adapter and then to the R, G, W on the Control Board.

Has anyone dealt with something like this?

The other white wire coming from the outside AC condenser typically connects to C, but it appears to going to ground. Maybe true C is also tried to ground?

If it were me, I’d use the unused blue wire adding it to the white/green/bare bundle, then tell the app you have C and connect the blue wire to C on the Wyze thermostat.

I’m just wondering, what is the blue wire supposed to do? If I connect it to what looks like a ground I am thinking this would not work.

It’s not uncommon to have unused wire, your current thermostat didn’t need a C wire so it wasn’t used. As a test, you could connect the blue wire as I mentioned and connect the red wire to Rc on the Wyze thermostat and see if it powers up.

I don’t see the white from the central air going to that green wire nut, I see it going to a blue wire. The red wire nut with green wires going to it is system ground, the wire nut size used looks like it is part of the incoming line voltage, not a thermostat connection, and the bare ground wire reinforces this perception.

If my perception is correct, and the white wire in the blue wire nut with the blue wire is also going to the A/C unit, then all you need to do is untwist the blue thermostat wire and strip the end and add it to the white and blue wirenut, then add it to the C terminal on your wyze, telling the wyze that your “old” thermostat has a C wire.

Speedier, sorry I made a mistake in my description. I looked at these wires so many times that I confused myself. The white from the Central Air does actually connect to the blue wire as you said, but this blue wire then goes to where the green wire is connected to the blower frame and apparently a ground as the green wire then goes back from here and is connected to the bare copper and a green.

If you look at the transformer, you should see one of the wires on the 24V side is red and one is blue. The fact that it is tied to chassis ground just means that they’ve chosen to ground one side of the transformer, it doesn’t have any bearing on where you should connect the wire. If you connect it in the manner that I posted, it should work fine.

Thanks for your help. I looked through my photos and it looks like you are correct. The transformer has 3 blue wires coming off on one side and a red wire coming off the other side. I am going to open the panel again today and look at it again to make sure. So if this is the case then just wire the blue thermostat wire to the wire but you marked as “C”, correct? The rest should pretty much be the same as they already are.

Use a multimeter, set to AC volt and measure
R and blue wire. Marked C by Speadie.

If it is 24v, then yes.

Ok, good idea. I did that and got a reading of 27 V. This could be a little off due to the quality of the meter or the older transformer might be a little off. I have wired a lot of stuff in my life but I’m very far from being an expert. Will the voltage being slightly higher have an impact? If not I’m going to give this a try because it seems this is where it needs to be connected.

10%over is still ok.
Just label your wire knobs for future references.
Already U have a wire from Tstat for C… You do not need Wyze adaptor.

Thank you everyone. It appears to be working. Tested it and both AC and heat seem to work.

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