Wyze thermostat install- No C-wire

I am attempting to install my new Wyze thermostat, but I do not have a c wire or access to my HVAC Furnace to add the adapter. I live in an apartment complex, and my current thermostat is battery-powered, so there is no need for the c wire. I have a W, Y, RC, and G wire connected to my current system.

Once I removed the thermostat and pulled on the wires, I found that there were a few more wires that were cut short and hidden. I have blue, black, tan, and orange wires in addition to the wires above.

Do you think that any of these additional wires can be used as the C wire? Any help would be much appreciated.

Welcome @kevingamez33 , I am not an HVAC person, but if one of them were a C-Wire, I would expect that the Blue or Black would be it. One of these are normally common for the 24v power and possibly more the blue. You may be able to check the wire with a tester to see if it has voltage on it. It may, but you normally would not leave it live and push it in the wall, at least without the proper protection on it.

If none of those work, you can get an adapter to plug into an outlet, if one is near it.

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I think this causes issues with getting some functions to work… I researched this for my install, but fortuntely while not the “text” book case I found a solution to my install which does NOT use the C Wire Adapter, nor an external 24VAC adapter…

As I recall doing this caused either Heat or AC not to work, and I want to say AC so I immediately dismissed this… Since well I need AC more than heat…

I will see if I can find the link that outlines this, but I am pretty sure the EXTERNAL ADAPTERS to power things are not viable or suggested.

NOTE: I too am not a HVAC Tech or person, did not stay at a Holiday Inn Express, or play one on TV. :slight_smile: :wink: :stuck_out_tongue:

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YES, it is POSSIBLE… This was/is similar to my case… I prepped by checking Tstat location, furnace and wires connected on board, and at the tstat…

I’d went as far as getting more a run of 2 wire Tstat cable to fish through for a C wire… I was halfway to doing it when I ran into another issue…


EVEN 24VAC can be dangerous and lead to many many bad things!

You need :
1 - Digital Voltmeter - any “home” store has these, even Harbor Freight is OK… for what you are doing… GET DIGITAL, NOT an old analog one!

1 - Wire strippers - any “home” store has these, even Harbor Freight is OK… for what you are doing…

Possibly you need to get some “test” leads to clip on the wires and test probes of your meter. It makes life a lot easier.

Carefully pull out the cable bundle… cut the sheath back to expose the other wires… DO THIS VERY CAREFULLY SO AS NOT TO CUT OR NICK THE OTHER WIRES!!!


The BLUE WIRE is the C wire


CAREFULLY strip the BLUE WIRE back after exposing some from the bundle.

Once you have this stripped

SET your METER TO AC Voltage use an appropriate scale, based on your meter… If you have it a 60V MAX setting is best, but some only do 200 or 400VAC… Either is fine…

PUT your test leads on the RED WIRE and the BLUE WIRE… DO NOT LET THEM TOUCH! ! !! ! Clip the leads to your meter probes… DO NOT LET THEM TOUCH! Polarity is not important here, like DC.

You want to get 24VAC plus or minus a little bit 23.5-26VAC is good… If you get that… then connect the BLUE WIRE you stripped off into the Wyze TStat.


If the wire is really cut short, you may have to make a jumper… You can get small short sections of TStat wire at “home” stores, and the old timey Ace “hardware” and others… and for a short section they may just give it to you… Use some AC WIRE nuts to make the connections. Be sure this WIRE IS AC RATED and 18 GAUGE is the norm pretty much… I had to make some jumpers at the TStat end and just cut some of the spare Tstat wire I had got if I had to run a new run.

This is similar to the setup I had to do… I had EXTRA WIRES to use in the cable already pulled… a few off this topic adjustments, and I was in business with out pulling a new cable or additional cable, and with out use the CWA which as an out period for me… not important why here… not an option.

Again, if you are not comfortable or even have BASIC AC electric wiring knowledge, I would get some one who is a DIY or professional to do this… AC is not something to play with! You can INJURE YOURSELF, CAUSE DAMAGE TO YOUR HVAC and more!

I work in HVAC occasionally, and the blue wire isn’t always C. really, the wiring can be whatever people decide to use. Yes, there are common wiring themes or guidelines that are usually followed by professionals, but in the case of apartments or other places where the person who installed the thermostats might be just a handyman, it’s quite possible to get completely reversed wiring.

I’ve personally seen the following uses for the blue wire: common, reversing valve, hot water valve, cold water valve, emergency heating, draft damper/outside air mix, recirculating pump, and a/c compressor.

That’s why without pictures of the system, I generally refrain from giving out guidance. Unless I can pretty definitively figure out how their system is wired, or walk them through the steps needed to determine that, I wouldn’t want to be responsible for knocking their HVAC system offline in case they connect something incorrectly.

In this case, I’m not giving install advice, as it is a multi unit apartment complex that does not likely have sufficient current to drive smart thermostats in every single unit and the tenant does not have the ability to reset or replace a fuse if they misconnect something.
I’d recommend that they contact their landlord and schedule time with the repair-person to determine if they can connect their thermostat safely.


That is the case in many cases… and any one who is not following the standard should get a trip to the woodshed for some remedial training. :slight_smile: :stuck_out_tongue: :smiley:

I can attest that if I catch up with the bozos who did stuff I’ve had to deal with they are going to wish they had taken up a different career path! As well as the ghost of my electrical instructor who would have some things to discuss over some of this! He’d have FAILED them on just the one GFI issue I’ve had.

In my case the C wire in the tstat cable is DISCONNECTED some where in the path between the controller and the tstat… Where or why??? :man_shrugging: I have no clue… THANKFULLY I found that the spares in the tstat cable did go from tstat side to the controller… I hijacked one of them at each end and all is good!

And its a good thing as I would never have gotten a another run of cable to make a C cable in there… The way its routed is absolutely bone headed… Bone headed…and that move potentially could have meant some issues in getting the tstat mounted up… Thankfully this was curable…

And NO I would not have used the C wire adaptor… That was ruled out from the start… That is just a janky solution… Not going to happen here.

Again if I catch up with the bozos who did stuff I’ve had to deal with they are going to wish they had taken up a different career path!

While I understand, and can agree with some of… I personally don’t like when I get to a thread like this with a problem like this, and don’t get help…ie: answers… “Hey its possible, but you should understand there are risks, to you, HVAC equipment, etc… …”

I am NOT an HVAC person… I do have education in electrical, electronics, and do stuff in a related field… RF in specific field. I have the basic knowledge of this, which is why the disconnect of the C wire in the cable make no sense… None…

I think I sprinkled in enough warnings about potential issues to the person, and/or the the equipment ie: HVAC parts to let them make a decision… I also know that when dealing with landlords this can be an issue… Case in point… my first apartment many decades ago… had electrical issues, as in a shared circuit that was causing issues… I just skipped the landlord… buddy was an electrician… for the cost of the parts, some beer and pizza… I got this resolved by running a new dedicated circuit that was not shared… Problem solved. Done to code. But I am sure that whiney landlord dude would have rejected this, I just skipped this drama…They never knew till I moved out, and after the place had changed hands as well… and I was long out of state. No forwarding info left. So they were free to undo it… by pulling out the new cable run, connect the old wires back. Which I wouldn’t the wiring in there was junk. MY NEW circuit stood out…

The point is that there are many issues like you listed incorrect wiring ie a BLUE WIRE that doesn’t comply with the standard… BUT it doesn’t hurt to pull the cable out, strip it out, and measure… IF, IF you get 24VAC from the RED and BLUE wires… I’d chance it that it is wired in compliance with the standard… If you don’t get 24VAC on this, ,then its game over really. So it don’t matter whats its wired to. That leaves that possibly it doesn’t provide enough power… but considering that this whole method of getting power any way has to be very low power to start as this was never the intention of it.

This brings me to the point that Wyze and ALL the other of these fancy schmancy tstat should have DEDICATED 24VAC ports to run them for the case when this power is not available. That way the janky C Wire adaptors can be tossed, and people can go to their desired source get a 24VAC power supply, and power this thing… I actually looked at this as I have an outlet close enough that I could do this… BUT you can’t do that as since wiring into Rc and C will cause something, as I recall AC to either come on CONTINUOUSLY or NOT AT ALL… So nope not an option.


Again, I get where you are coming from, I just don’t happen to agree 100%.