Taco ZVC404: locating C question

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Old 11-08-19, 07:40 AM
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Taco ZVC404: locating C question

What do you do if the live 24vac does not have the common labeled? I have the older version of the TACO 404-4. The TSTAT posts are labeled T T and the left side has the red wire and right side is the white wire. The live input from the transformer has two yellow wires. Can I just measure from the red TSTAT wire to determine the common side of live input? I have two TSTATS that are both functioning fine right now. My basement TSTAT (zone 2) has an external 24v transformer installed for the c wire. My main TSAT (zone 1) has three wires in the wall behind the TSTAT but only the red and white are connected.I am trying to determine where to connect this third wire at the TACO controller but don't want to mess anything up. Thank you for the help.

Name:  TACO  zvc 404.jpg
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Last edited by PJmax; 11-10-19 at 12:44 PM. Reason: updated diagram
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Old 11-09-19, 12:13 AM
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Welcome to the forums.

I'm glad you checked first. It's easy to burn up those controllers. The stat connections are TT. There is currently no assigned R and W. Someone randomly connected the red and white wires there. With a two wire stat...... there is no connection priority as it didn't make a difference. It makes a big difference now.

Using the picture.............
Remove the wires from zone 1.
Short the zone 1 TT connection with a short piece of wire.
Measure from that shorted connection to the power in terminals. One terminal will measure 24vac. Mark that terminal as C. The other one will be R.
Now...remove the jumper.
Measure from C to either TT terminal. The one that shows 24vac gets labeled as R.
The other T terminal gets labeled W.
Now you have R, W and C for your new stat. The same labels will apply to Z2 and Z3 and etc.

Let me know what you come up with.
 
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Old 11-10-19, 06:53 AM
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Here is what I found:

Left post of 24vac input is red and right is common.

Left post of TT is white and right post is red.

This is the opposite of how the stat wires were connected.

I have changed the stat wires to the correct orientation. Thank you for the help.
 

Last edited by kadayo; 11-10-19 at 08:41 AM.
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Old 11-10-19, 12:45 PM
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This is the opposite of how the stat wires were connected.
That's because with only two wires it makes absolutely no difference.

Thanks for your help. I've updated your original post to reflect the modified diagram.
 
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