Thermostat C wire connection on Trane

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Old 03-09-19, 02:14 PM
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Thermostat C wire connection on Trane

I purchased a Honeywell RTH6500 Wifi Thermostat, which requires a C wire. My old thermostat showed a connected blue wire to its C terminal. However, it was battery-powered. If I removed the battery, the thermostat screen would go dark. This is pretty close model of my old thermostat:
https://pro.luxproducts.com/wp-conte...NG_Manual1.pdf.
Below is a picture of my old thermostat wiring.



After I connected the RTH6500, I measured with a multimeter, which showed 0V on the C terminal. All the other connected terminals showed positive voltage. I went up to the air handler and saw there was a unconnected blue wire.



I'm guessing the three sets of wires are going to the (1) air handler, (2) heat pump, and (3) thermostat. You can see the green wire is also unconnected on a different set (branch). The green wire on the thermostat is connected to G terminal, which I think is the fan. I think that set of wires is probably going to the heat pump, since it doesn't have a fan?

After getting some help from another forum, I opened up the air handler, expecting to see a C terminal for common, but I only see the blue wire connected to a B terminal. I looked at the new Honeywell thermostat's wiring diagram, and it shows B can also go into its C terminal. I'm 90% ready to go ahead and strip the unconnected blue wire and add it to the wire nut connecting the other two blue wires. I just want to get some opinions before I do it.



FYI, I have two air handlers and two heat pumps. The air handlers are Trane TWE030C140F1 and Trane TWE 042C14FB1. The heat pumps are Trane TWR042C100B2 and Trane TWR030C100A4

Thanks for any guidance you can provide.
 
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Old 03-09-19, 02:55 PM
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Welcome to the forums.

On a Trane unit..... the B is the same as C. Connect all three blue wires together in that splice.
 
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Old 03-09-19, 07:17 PM
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Thanks PJmax. I did that and my new thermostat now has power.

I'm now trying to program my thermostat, and I originally set it to "Heat pump WITHOUT backup or auxiliary heat" because none of the W1/W2/W3 terminals at the air handler were connected. However, I just read this thread, https://www.doityourself.com/forum/t...tween-y-w.html. The original poster and I both had Y jumpered to W on our old thermostat, and the recommendation there was to select heat pump WITH backup or auxiliary heat, so now I'm not sure anymore.

Can anymore provide guidance here?

Thank you
 
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Old 03-09-19, 08:46 PM
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There is no jumper required and you do not have back up heat. You must be in a warmer climate where only minimal heat is needed.

Red ----> R/Rc
Blue ----> C
Green ----> G
White -----> O/B and programmed for O to cool.
Yellow ----> Y
 
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Old 03-10-19, 11:09 AM
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Yes, I live in Phoenix, Arizona. So, following your advice, I will set my thermostat to the function in the green box and not in the red box.



Can you please me your blessing? Thank you.
 
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Old 03-10-19, 12:13 PM
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Yes.....use choice #1 in the green box. Consider yourself blessed. Name:  smiley-thumb - S.gif
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Old 03-10-19, 01:48 PM
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PJmax, thank you so much for your kindness and patience.
 
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Old 12-17-20, 12:31 PM
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trane package heatpump

I'm trying to wire a new orbit thermostat to my trane package heat pump. I have a blue wire from the heat pump but no "B" or "C" terminal on the thermostat. Should this blue wire land on a different terminal?
 
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Old 12-17-20, 12:59 PM
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Welcome to the forums.

Always take a picture of the old when making a change.
I like to see a picture of the old posted here..... How-to-insert-pictures.

What terminal was the blue wire connected to on the old stat ?
If you are installing a battery operated stat..... you won't need a C wire. Tape it off.
 
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Old 12-17-20, 01:36 PM
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thanks for your response Pete, I messed up and didn't take a pic of the old thermostat wiring, all the wires were at the appropriate terminals so I figured I could just reinstall as same in new thermostat....the blue wire wasn't used on the old thermostat, but when I traced it to the heat pump it was wired in. The new thermostat requires batteries , so I assume it is battery operated. The heat pump works as wired without the blue wire ( heating and cooling) so your advice must be correct and I will tape it off....thanks so much for your advice..
 
 

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