Wyze Thermostat issues - not detecting y and g wires

[hvaldes]

I tried setting up my thermostat but for whatever reason, it won’t detect my yellow and green wire so it won’t turn on the AC at all. The thermostat does have power. I have tried reconnecting it a few times, took it off and put back my old thermostat and the AC turned without issues. This is so frustrating, there is obviously power on the cables but it won’t detect them at all. What else can I try? I do have an old system without a computer board.

skipping in the setup did not work, my AC won’t respond to any settings through the wyze thermostat but the old dumb thermostat works without issues.

[speadie]

Please take the following pictures and share here (higher resolution is better):
Old thermostat wiring
New thermostat wiring
Furnace/ Air handler wiring (the other end of the thermostat wires, and where they go)

[hvaldes]

If I put everything back to the old thermostat everything works.
I can’t take a picture of my AC unit, it’s on the roof but it doesn’t have a computer board. I used the 24 v adapter to get power to the wyze thermostat and that works. I have tried the wireing with the jumper cables as well as the instructions on the adapter say to do that. It still won’t detect the Y and G wires no matter what.

[hvaldes]

[speadie]

Unfortunately, due to the internal wiring in the wyze, you cannot use it for cooling if you are using a wall adapter to power it.

Wyze thermostat simplified block diagrams

I made a couple of simplified block diagrams to show why running the wyze thermostat requires a C wire and why if you use an external transformer, you cannot use the Cooling aspects of the wyze. Not sure if this will help anyone, but it’s worth trying. Current needs to flow through the R and C terminals of the transformer, through a load in order for that load to get powered properly. Without a complete loop back to the transformer, you run the risk of the current finding its way back through…

[Ken.S]

use the c wire adapter instead of the external transformer, you have enough wires for the adapter

[hvaldes]

@Ken.S

se the c wire adapter instead of the external transformer, you have enough wires for the adapter

I can’t my AC doesn’t have a computer board, plus it’s on the roof. I had an AC guy already try to make it work running the C wire but the wyze would not power up. I’m about to give up and buy a nest instead.

[Ken.S]

gotcha…though just because it doesn’t have a control board, doesn’t mean it wont work. your red Rc wire is getting it’s power from a transformer somewhere, that transformer also has a C common side…you just have to find it.

[hvaldes]

We thought we did, but when I connect it to the wyze thermostat it doesn’t power up. R to Rc, C to C, but it didn’t work. I didn’t see the connection on the other side, but my AC guy said it was there. I actually have the blue wire at my terminal though it wasn’t connected to my old thermostat. So frustrating.

[speadie]

Your ac guy should have tested between Rc and C at the thermostat to determine that there was at least 25VAC present. Often there are splices in wiring, and they only hook up the wires that are actually in use. Most likely, there is a splice somewhere in your attic where the blue wire is interrupted if the C wire is not carrying voltage all the way to the thermostat.

[hvaldes]

Thanks for the tip. We didn’t check that. He did ask me if there was a crawl space in the attic later on but he hasn’t been able to come back to finish. This must have been why he asked. I was hoping that the external transformer would let me by pass this and not have to call him to come back. I was happy buying the wyze thermostat because of it’s price point but turns out it’s going to cost me a lot more with my unit being on the roof.