Hi all. This is a general HVAC wiring question so appreciate everyone’s patience.
I purchased some 2gig CT100 z-wave thermostats. The kids’ bedrooms are on what seems to be slave thermostats, that connect up to a master thermostat in another room that has B and O wiring (which may control dampers etc, but effectively has an ON/OFF (heat, cool, off) switch and has to be on else the kids’ thermostats don’t have power). The kids bedrooms have non-programmable, Honeywell Round thermostats that use only W, Y, and R wires.
I need a C wire for the CT100 to operate as a z-wave repeater, so found a zone controller in the attic that controls the scheme above. However, it seems as if the controller is an old one. There are already extra wires that are unused, so can connect an unused wire between the controller and the thermostat,… problem is that the zone controller doesn’t have a “Common” screw terminal.
There is a nearby 24v transformer, as you can see in the photo. Is it ok that I simply take an unused blue wire as an example, and splice the 24v source, and then connect the other end to the thermostat? If I do that, which wire do I splice from the transformer, red or white,… from the photo, there’s a lead that is red and reads “Load”, and then there’s a white one on the other side.
The controller board is labeled Trol-A-Temp 422044 rev,… so i’m not sure if it is a MM-3 MASTERTROL MINI-ZONE-3 or MINI-ZONE 2. I know that newer boards have a R Y W G C … the Trol-A-Temp that I have only has Y R W terminals where the kids’ thermostats would connect. There does seem to be a little switch that has a C and O setting, but I don’t know what terminals those refer to. Those brown wires on the far right of the control board don’t go to the bedroom, only the white ones in the center of the board.
Thanks in advance for your help.
On a thermostat … the R and C wires are connected to the transformer to get power.
I see there is a red wire on the transformer … if you trace it does it connect to the R wire on the thermostat ? For sanity it should!
If you are not sure … do not worry … assume it does …
Use an extra wire and connect it to the white wire on the transformer and the C wire on the thermostat.
It will not hurt anything if you end up connecting this to the wrong wire! You just will not have any power to the thermostat.
If you have no power on the thermostat … just move the extra wire at the transformer to the red wire … but as I said … If sanity prevails … you should not have to do this.
On the round Honywell thermostat when it calls for heat … the R and W are connected, when it calls for cooling, the R and Y are connected.
Wow, thank you RichardTSchaefer, the author of VeraAlerts! The privilege is all mine!
Will try as you suggest when I get home. Was going to offer up the schematic below but seems it was not needed.
I’m thinking I should even just screw the extra wire to terminal 1 on the image below (in red circle) and avoid using a wing-nut all together.
Hopefully, there are no load problems. I read in another forum, where the individual had to add a separate 24v tranformer for each individual thermostat!
Thanks again.
Still not enough details on the internal of the controller to know for sure …
But your plan is in line with what I would do … and if it does not work … them move it to #2.
I have had lots of jobs in my lifetime … A few years while going to college in my father’s HVAC business doing installation and service.
Ok, so I went ahead and connected an additional wire to the 1) terminal (where 24v white wire meets zone controller board).
At the thermostat, my multimeter tells me :
-24v across the R and W
-0v across the R and Y
-24v across the C and W
-0v across the C and Y
-0v across the R and C
Not sure if this is as it should be, but when I remove the batteries, the thermostat shuts goes out (screen off, no power).
This is in contrast to my other CT100 installed downstairs that stays on even without batteries. The only difference between them is that the one downstairs shows:
-24v across R and C
there’s also a G wire
The downstairs thermostat connects to a different zone controller, one that does have C terminals, etc. Not the old Trol-A-Temp like upstairs.
Did I do something wrong?
Nevermind. Richard was right. I went back to the controller, and simply attached to terminal 2 (load side of where 24v connects to board) instead.
Everything is working as it should.
-24v between C and R
-24v between C and Y
-0v between C and W
Thank you so much for your help!!!
The change above helped me to get through the winter months, but alas, now at the height of summer, the wire configuration is preventing me from activating the air conditioning compressor. The CT-100 thermostat would kick into compressor protection mode/timeout, and the room would never cool down.
Only by undoing the 24v piggybacking above can the zone controller now kick off the compressor and keep it on.
I suppose that there is a load issue by trying to share that 24v with the C wire?