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C wire hook up on the TACO box

BrokenOldBottle
Community Member

I have an existing thermostat running on two wires with batteries and I want to replace it with a nest thermostat that requires a C wire. I do have a third wire available to me I just need to know where to hook it up on the TACO Box

1 ACCEPTED SOLUTION

laurentbourg
Bronze Product Expert
Bronze Product Expert

There is a C connection hub, typically located on the left hand side of your Taco, it might also say 24V. What is the exact model of your Taco control module?

View solution in original post

64 REPLIES 64

laurentbourg
Bronze Product Expert
Bronze Product Expert

There is a C connection hub, typically located on the left hand side of your Taco, it might also say 24V. What is the exact model of your Taco control module?

View solution in original post

Thank you I'll pull the cover off and check which model I have but I think that answers my question

I have an older system two wire. I have no circuit board. Has Honeywell RA832A with (3) zone valves. transformer on top of 832. I have extra wires not being used in my thermostat  & was planning on using one of the for my "C" wire. Just not sure where to connect on furnace side? wasn't sure if i should hook to transformer 

laurentbourg
Bronze Product Expert
Bronze Product Expert

Please upload pictures of your setup

PXL_20211206_225839471.jpg

PXL_20211206_225805529.jpg

PXL_20211206_225812447.jpg

I called TACO in Rhode island and Steve in Tech Support walked me right thru it.

PXL_20211206_225805529.jpg

PXL_20211206_225812447.jpg

laurentbourg
Bronze Product Expert
Bronze Product Expert

I have reviewed your pics, and confirmed you should be able to tap the C wire on your 24v  transformer that is on top of your RA832 controller, connect it where the white wire is connected. 

Connected directly to the white wire on the transformer or follow the white wire off the transformer

laurentbourg
Bronze Product Expert
Bronze Product Expert

connected directly to the white wire on the transformer. It is a 24V transformer, correct?

Correct it is. Also if I add another nest thermostat for a different zone in the house can I add another wire on the white side of the transformer

PXL_20211207_001519774.jpg

 use the green as my c wire to white on transformer. The Old wire that was coming behind the thermostat that runs down to the junction box I connected to that. When I measure up at the thermostat I have 18 volts? 

laurentbourg
Bronze Product Expert
Bronze Product Expert

When you measure R to C at the thermostat, so red to green (I assume your R is red), you get 18v AC? how about when you measure R to W?

when I measure r to w=26

R to C =26

laurentbourg
Bronze Product Expert
Bronze Product Expert

Ok good, you should be all set. Go ahead and install your Nest, let me know if any issue. 

Thanks again I really appreciate the help 👍👍

laurentbourg
Bronze Product Expert
Bronze Product Expert

Anytime. Please mark the answer as a solution when you get a chance. 

Very weird I have it wired with the proper voltage but the nest display still says c wire not getting enough power

Depending on the age of your TACo box it may be required to reverse your red and white leads inside the switch coming from your thermostat. red has to go to the right lead even though they're both marked T

Yea I'm at a total Lost. At thermostat R to w =26v

R to C =26v

Nest says lost voltage on c🤔

laurentbourg
Bronze Product Expert
Bronze Product Expert

Check your wiring diagram in the settings on the Nest, everything looks good and matches physical config?

I will double check I have R.W and C hooked up on the thermostat. I will double check settings

laurentbourg
Bronze Product Expert
Bronze Product Expert

Ok let us know, sometimes the Nest gets confused and physical does not match software, so important to always make sure. Also you can look at the power section in the settings -> equipment -> tech section and also check other info to make sure it all looks good. 

laurentbourg
Bronze Product Expert
Bronze Product Expert

How is it looking?

Call TACO, they are really helpful

If I install another nest to the second zone. Can I use another c wire on the same spot of the transformer?

1638833732845356965659236681161.jpg

 this comes off the transformer I have 19 volts here but I have 24 across the transformer

Thekideo
Community Member

Looks like a mess but it's a pretty straightforward mess.lol bear with me I'm trying to figure out how to upload my pictures

laurentbourg
Bronze Product Expert
Bronze Product Expert

you just click on the picture icon available in the textbox when you reply

Hopefully my pictures went through. When I take the cover off the junction box it looks like all the whites are twisted together. I had an extra wire behind my thermostat not being used I was going to make that my c wire. Just wasn't sure where to do the hook up by the furnace

PXL_20211206_232220457.jpg

PXL_20211206_232229582.jpg

Double check my wiring and everything seemed to be okay. For some reason now the screen is stuck in setup mode. It won't even let me reset the screen. I decided to take it off the wall and take the batteries out to see if that will help. I will hook it back up tomorrow and check to see what I got going on. Thanks again I'll let you know how I make out

laurentbourg
Bronze Product Expert
Bronze Product Expert

Ok good luck

laurentbourg
Bronze Product Expert
Bronze Product Expert

You can also access your wiring diagram from the google home app in the thermostat settings. 

Set the thermostat up but for some reason it's still not seeing the C wire