No circuit board for Wyze Thermostat

I just received my Wyze Thermostat. I did the survey before I purchased to make sure it was compatible and it said my system was. However, I am at a standstill.

I only have a 4 wire system, and it tried to walk me through the steps to connect the C-connector to the circuit board.

My system doesn’t have a circuit board. My house is a 18 year old Palm Harbor home with an air handler system. The existing 4 wires are hardwired with wire nuts into the system.

I am extremely familiar with my system since I replaced every electrical component in it about a month ago.

What do I do?


Mine old hot air furnace doesn’t have a control circuit board either, but on mine, there are multiple connections right on the 24v transformer itself. Each connection has a hard to see stamped letter for C, R, G, etc.

Is it possible you have something like that? Here’s mine


Thanks for response, but mine doesn’t have that. Here are the pictures of what I have.

I also have a contactor that looks like this:

Here’s a picture showing where my thermostat 12v wiring is hardwired to the 24v wiring.

You can see the thinner wires connected with wire nuts.

The purple and blue wires coming off the top of that 24v transformer in the first picture. One should go to the red wire, the other should be common. Just watch out, because you appear to have high voltage lines that are the same color and size as the low voltage lines in there. Make sure you trace it from the 24v side of the transformer to the wirenut.

There isn’t a blue wire. It’s a gray wire.

Here is a description of where of where the wires coming out of my 24v transformer go as well as the rest of the 12v wiring from the thermostat:

Top left wire is Purple. It leaves transformer and connects with a wire nut to 12v Red wire coming from my thermostat.

Top right wire is Gray. It leaves and connects with a wire nut to a White wire which is one of the 2 wires in the brown wire which goes under the floor (maybe to the outside AC unit?) See below picture:

As you can see, there is another wire in the 2-wire bundled Brown wire.

The Red wire section of brown wire (going under the house) is connected with a wire nut to the Yellow 12v wire coming from the thermostat.

There is a White 12v wire coming from the thermostat that connects with a wire nut to a white wire directly wired to my heating element. In the picture below, the bottom left yellow wire nut is this connection.

The last wire from my thermostat is the 12v Green wire. It connects with a wire nut to a green wire that is wired into a general purpose relay switch.

I hope this description makes it easier to understand. Whoever installed this is the most unorganized person. It looks like a huge mess of wires.

I am grateful for any help!

The thermostat is 24V, not 12V. All low voltage control components in a HVAC system run on 24V.

I think you should connect your thermostat adapter wire as follows:

You want to make sure all power is off to both the inside and outside units before unscrewing any wire nuts. Have extra wire nuts of the proper size handy, and wire strippers, in case a wire breaks off in the wire nut when you unscrew it. Also, make sure you have a flat screwdriver small enough to fit into the terminal strip on the wyze adapter.

Remove the wire nut from the gray and white wire and insert the C wire from the adapter into the connection and reattach the wire nut (Note: this is the only case where you are only adding a wire, not removing any from the wire nut).

Remove the green thermostat wire from the green wire wire nut, and attach the G lead from the adapter to the green lead from the fan switch with a wire nut. Attach the green thermostat wire to the G terminal on the adapter and tighten the screw.

Remove the red thermostat wire from the purple and red wire nut, and insert the R wire from the adapter into that wire nut with the purple wire and tighten. Insert the red thermostat wire into the R terminal on the adapter and tighten the screw.

Remove the white thermostat wire from the white heating element wire nut, and attach the W lead from the adapter to the white lead from the heating element using the wire nut. Insert the white thermostat wire into the W terminal on the adapter and tighten the screw.

Remove the yellow thermostat wire from the red and yellow wire nut, and insert the Y wire from the adapter into that wire nut with the red wire and tighten. Insert the yellow thermostat wire into the Y terminal on the adapter and tighten the screw.

This should allow your Wyze thermostat to get a solid 24V connection even without a dedicated common wire in the thermostat wiring.

Ideally, instead of the rats nest of wires, the installer would have used a terminal strip to get all the wires in one place, and then used zip ties to clean up the wiring loom so that it wasn’t so hard to see what was doing what, but unfortunately some people are too rushed to do a good job.


Thanks for the quick reply. You said

There is no C wire on the Wyze adapter. The only wires are labeled Y, W, R, and G.

1 Like

There should be 5 wires on the adapter, 4 white, 1 gray, with 4 terminals for attaching to thermostat wires. C is the grey wire.

Mine looks exactly like this, and then I have only two wires coming out from the wall at the thermostat. Do the blue, green, and yellow wires from your transformer in that photo all go to your thermostat?

1 Like

Thank you, thank you, thank you. Your instructions were clear and easy to follow. I just finished setting up my thermostat with ZERO problems. The test ran perfectly also. Everything is up and running thanks to you.

BTW, Wyze hasn’t even acknowledged my support ticket on this issue yet. I got tired of waiting and tried the forums in the meantime, and you solved it!


The only two wires coming from my transformer are purple and gray. Each of those I had to follow his instructions and connect to my thermostat wires, as well as the other thermostat wires I had to connect.

I suggest taking pictures of your exact setup and posting them. That should make it easier to find your solution.

They do now. Years ago, I only had the two red and white wires hooked up that go to another control box on the furnace. Those two wires went to a plain non powered mercury thermostat. It simply turned the heat on or off. Then at some point a few years ago, I wanted a programable thermostat to run a schedule and also to run just the fan if I wanted. So I hooked up the ones you saw in my picture so I could do that. When I just got the Wyze, I only had to hook up the C wire on that transformer and I used the yellow wire for now since it’s normally used for cool and I don’t have AC.

Perfect. My exact same situation but just with a hydronic boiler. But same setup. Looks like I just need a 3rd wire and I’m good to go. Pulling shouldn’t be a problem. Thanks!!!

Pulled a 3rd wire. Hooked it up to Common. Works! Thanks so much!

1 Like

Can you / someone with similar setup post pics of the adapter connected? I’ve got the same thing going - old unit, no circuit board, and I want to get mine working!

I have red, green, blue, and white wires coming to my current thermostat. Having trouble tracing back to the air handler.

I’ve got a similar setup (no control board), see post below. I think I know how to wire in except for the C wire. Any help would be appreciated!

Wiring issue - no control board at Furnace for C-wire adapter - Ask the Community - Wyze Community (

Glad to her it worked out!

Post a picture or make a new thread and i’ll try to help.

I think I have the same issue. I have no circuit board or control board in my HVAC system. The wires that go to my thermostat is blue (Y), green (G), white (L), and red (R). Any help much appreciated!

Here is my post