C Wire required?

[StanGale]

Lots of conflicting information. Have a four-wire system and have been told that a C wire is necessary.

Others report you don't need a C wire.

One post said I could use the fan wire as a C wire.

Should I return this thermostat or can can it be successfully installed in another way. 

Thank you! 

 

[Houptee]

It will be much more stable and keep powered up with a C wire.

Do you have a extra wire in the cable in the wall that is not being used?

Normally there is a green wire that is used for fan but if no extra wire than you can use that blue wire as the C.

But you have to go to the furnace and move it from G screw to the C screw on the furnace.

This method will no longer let you turn on only the fan it will run the fan normally when heat or AC is on but not fan only anymore (most people never run just the fan anyway).

[StanGale]

Thank you Houptee. It's very clear that you know what you're talking about.

Unfortunately access to the furnace is extremely difficult because it's up in the attic crawlspace.

There's no other available active wires. System is from 1979.

We actually do use "fan only" because it's a two-story house and the heat stays at the top so running just the fan pushes the heat down.

Unfortunately, it appears I must return this thermostat.

[Houptee]

You can try it see if its getting suffient power after installing it.

You go to the Equipment tab and then Power Info. If it shows 24-30 V for Lin then you are ok without a C wire.

Usually problems occur with 2 wire heat only or AC only systems.

[EdwardT]

Hi folks,

@Houptee, thanks for the help!

@StanGale, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[EdwardT]

Hey StanGale,

It's me again. I wanted to check back in to see if you have other questions and concerns. Feel free to let me know if you do. 

Thanks,

Edward

[EdwardT]

Hi StanGale,

I'm just checking in to make sure that you've seen our response. Please let us know if you have any other questions or concerns as I will be locking this in 24 hours.

Thanks,

Edward