I am going to install a new Smart Thermostat and need help with were the C-Wire is supposed to go. I understand that it needs to be used on the unit I am getting and last night I verified I have the wire (not hookup up, but its there) from original date. My issue is with the wire, I notice I have a 5-wire setup and at the unit inside the house the blue wire is cut and wrapped around the wire and there is a green wire also wrapped. I have attached a picture of what I see and if you notice the G,W,R and Y from outside I guess is hooked up to the thermo wire but the blue and green on the thermo is not used. Also, I seen online that people had screw type terminals on a PCB but if you notice the white plug behind that brown fuse is where my identifications are for W,Y etc.. Now, with that being said the two brown wires coming out of that white plug are identified on the PCB and both locations on the PCB say C,C and they are tied together and go to a transformer behind them.

Long story short can I just take the blue wire from the thermo and tie it into the two brown wires going to the transformer? If not, is there a way to test with a VM to find out what I need to hookup to get the C-Wire usable>?

 

The large brown wire connected to the small red wire directly in the center of the picture should be C

That small red wire that connects to that brown wire should be in the cable that goes to the condensor. The other wire in that cable should be connected to yellow.

You should measure 24VAC between brown and red wires.... and between R and C at the stat.

 

Just got home and attached is what I see at the stat. I read 28v across from RC to white, green and yellow. Not sure I am doing that right. I will be able to hook up the new smart stat correct?

 

I read 28v across from RC to white, green and yellow...and to C after you connect it at the air handler.

 

All I did when i got home was take the stat off and put a meter to the wires. I don’t have the new smart stat yet and the unit was installed in 2010 and it has been working. I just figured to put a new stat in. Am I supposed to tie the blue wire in at the the air handler from the stat somewhere? I don’t need to mess with anything outside at the unit do I? I just want to know what I am doing when the stat gets here so I am not wasting hours trying to figure it ou, lol. And thanks for the help.

 

You need to check AT the air handler that brown is C. I told you what to look for.

Strip the cable at the thermostat and connect the blue wire to C.
Strip the cable at the air handler and connect the blue wire to the brown splice.

You can do this ahead of time but the blue wire cannot touch any other wire.
Always turn the power off to the air handler when changing any wiring.

 

Got you, the brown wire on the white plug connected to the PCM behind that fuse is going to pins labeled C on the PCB, from there the brown wire is going to a transformer. So, I will shut down power, connect the blue wire at the AH to the brown wire going to the transformer. Then I will connect the blue wire at the stat to the C terminal on the new smart stat. Thanks for the help sorry to be unclear on this, I just don't want to mess anything up. I don't take anything away from A/C techs and installers but I just don't have the funds to have them install something I can do myself with a little help.

Thanks
Wade