Installing Wyze Thermostat-no C wire

I just moved into an apartment with a crappy HVAC system. It’s a non-programmable basic Honeywell unit and I’d rather have the Wyze Thermostat on the wall. The problem is there’s no C-wire connected to the existing thermostat. The cable that leads to the air handler has an unused C-wire on both ends. I looked up videos on how to add the C-wire adapter, but those all seem to be for systems with some kind of control board or bus bar. My system has none of those, just some relays and transformers.

This would be a job for the C wire adapter, but I can’t find anything that resembles a C-wire terminal. My unit is a First Co 18HX5-240. Does anyone have experience wiring their Wyze thermostat to one of those units? Maintenance is backlogged and I don’t know if I trust them to wire it correctly. See pictures.

Need better image of this area.
That brown wire should be C, but I can’t see the wire connections clearly to make sure.


Get a Volt meter. Make sure it is on AC measure. Red volt meter lead to the brown wire and black lead to a good ground. You should read 24 - 28 volts AC. This will verify the brown as your 24V common needed for the thermostat. I just verified mine a couple of minutes ago.

Sorry for the late replies. I was able to find the C wire and connect it. Unfortunately, something happened which ended up with the thermostat making a buzzing noise and smoke came out. No clue what happened, but that thing is dead. I managed to get a good deal on another big brand of thermostat, so that’s the end of my Wyze Thermostat days.

That is a big ouch. So sorry that happened to you.

By the way, our schematics are identical.