Wyze thermostat turning on both AC and Heat in Heat mode

here’s image of my old thermostat wiring

Show how you wired the adapter. most likely you put your AC compressor on the wyze adapter terminals instead of leaving it on the furnace.
It should look like this: In your case the Y wire that goes to the AC compressor is red and the C wire that goes to the AC compressor is white.

correct wiring


Thank you for the diagram. Very helpful! Yes, I did put the AC compressor wire in the wyze adapter terminal instead of leaving it on furnace. Problem solved. Can’t thank you enough!

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how do you know what yellow wire has to stay on the furnace and what one goes into the adapter. i was having the same problem so i just took it off and put my old on back on.

Share a picture of your wires and I can tell you which is which. I’m looking for the wire bundle that connects to C and comes back as Y. That is your outdoor A/C compressor, and needs to stay on the furnace/ air handler.

So I am guessing that the wire harness For the ac only has two wires the red wire goes with the c and like the whitish yellow one goes on the yellow so I’m guessing that yellow stays on the furnace and then the second harness with all the wires that yellow goes into the adapter right?

if you can strip this back a ways, and splice a wire onto this blue wire, and connect the end to C, then you wouldn’t need to use the C adapter, you would just need to find the blue wire behind your thermostat and connect that to C.

But yes, the 2 wire connection stays on the air handler panel, and the labeled thermostat wires below go into the C adapter, if you use it.

I opened the Wyze adapter since I wasn’t using it (5 wires to my thermostat) and diagrammed the circuit.

The R lead is switched to G and to Y.


Right. W is a straight path through the adapter, nothing connects to it. I think they just put W on the adapter to make it easier/put all the wires in one place.

My daughter replaced a battery operated 4 wire thermostat with the Wyze thermostat. Followed the directions exactly, which required the C Adapter. But the AC came on, as well as the furnace, whenever the heat mode was activated.

Wyze requested photos of old thermostat wiring and new wiring, which we sent. Then asked for more photos… Never offered a solution.

We determined, with a multimeter, that the C Adapter and thermostat were sending on signal to Y wire in heat mode.

Don’t waste your time with a ticket. Use a spare wire in the wiring harness to run from C to C ( be sure to label it) and match the original wires as they were before.

I don’t think it affected heating, but it did use a lot more electricity than it should have using the C Adapter.

I had the same problem, what I found out was I was putting the y wire form my ac into my adapter instead of the sone from my thermostat. Find out what y is from the thermostat and put that into the adapter then the end of that y from the adapter put that one and the yellow from the ac onto the furnace and it should work

When you use the C adapter, it uses the Y wire to send both the fan signal and compressor signal from the thermostat to the adapter, and uses the G wire as the common wire. Therefore, if your compressor is in series with the thermostat run, instead of both the thermostat and the compressor being hooked up directly to the air handler, your compressor will run whenever the thermostat calls for the fan to run.

But you’re correct, whenever possible, it is best to use a real C wire.

Why would it use “Y” wire (cooling) in heatingmode,?

It runs the fan (G) using the Y wire when the C adapter is installed. The C adapter detects the fan (G) signal on the Y wire and turns on just the G wire, but if your compressor attached to the Y wire between the thermostat and the C adapter, it will also be turned on by a fan (G) signal.

Exact same issue here, but it’s not clicking in my brain. I have 4 wire to thermostat and a c-wire on the furnace board. I connect the c adaptor to associated colors and left the c wire (on board) where it’s at. I must be missing something. Any help is greatly appreicated.

I had to hook it up per the wizard (ac fan came on with heater), then wired thermostat the same as the heater (no adapter)

You’ve got your compressor in series with the thermostat. the fact that you don’t have separate Y and C wires running to the compressor tells me this. Find the splice point and i can show you how to add a wire to fix this problem. see this post. Wyze Thermostat Problem - AC on with Heat - #37 by speadie


Splice point?? And thank you for your time!!

follow the thermostat wires from your furnace to the point where it splits into 2 different wires- one will go to the a/c compressor outdoors, and one will go to the thermostat