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Elton20 09-08-2013 10:50 PM

Installing a new programmable thermostat?
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I would like a new thermostat in replacement of my current mercury one but there are no labels on the wires are anything so someone tell me how to do this?

moondawg 09-09-2013 12:27 AM

The wires are color-coded, and do not need labels.

There "should" be some small letters on the old thermostat near where each wire connects. "Y" for yellow, "R" for red, "W" for white, and so on.

If there are NO markings on the thermostat, then my best advice would be to go open the cover on your air-handler and see how the wires are connected.

Again, there should be letters on the terminals where the wires are connected. As long as the wires are correctly wired at the air-handler, return to your thermostat and wire it up accordingly. If the wires are not hooked up correctly, take this opportunity to fix it. Turn off the breaker for the air-handler, and move the wires to their correct terminals.

The new thermostat will have the terminals labeled. If you happen to be color-blind, get someone to help you.

Sometimes, there is an "extra" blue or black wire in the bundle. This is supposed to be used for the "common" or return path for 24V power. Many times this did not get connected because it is not necessary for older thermostats. Modern thermostats may be powered by this 24V power and need the "common" to be hooked up. If the wire is there, hook it up.

Good luck.

beenthere 09-09-2013 04:38 AM

Remove the stat from the base plate. There will be terminal designations on it. Label which wire went to which(not everyone uses the same color codes). Yours may have a wire on a terminal labeled T, it will not be used with your new thermostat.

You can always take a pic of whre teh wires are connected, and post the pic for us to see, and help you.

PS: It helps to know the brand and model number of your equipment, if it isn't the original Trane equipment anymore.

biggles 09-09-2013 07:17 PM

if you see a "C" on the new subbase you need to run the other side of the air handler TR up there to have a solid 24V to run the new programmable...manual will tell you about it

Elton20 09-09-2013 07:38 PM

It's really weird
The wires are soldered to the mercury tubes so idk whats up.

firedawgsatx 09-09-2013 07:53 PM

2 Attachment(s)
If I remember correctly you should be able to remove the face plate of the thermostat by removing the silver screws and you can access the wiring terminals as shown in the photo

beenthere 09-09-2013 08:03 PM

Look at the thermostat, see those recessed screws. turn them out.

bobelectric 09-09-2013 08:19 PM

What the? It looked like my Lennox stat I changed out.

Elton20 09-09-2013 10:29 PM

Thanks! Fire
Thanks so much fire that helps. But will a regular stat have enough places to connect all those wires? Looks like 6-7 wires

beenthere 09-09-2013 10:34 PM

A heat pump thermostat will.

firedawgsatx 09-10-2013 08:43 AM


But will a regular stat have enough places to connect all those wires? Looks like 6-7 wires
Your system may not have that many wires unless it is a heat pump (as beenthere stated). The photos I posted do have a lot of wires because it is a heat pump. Once you remove the front and the base of your thermostat you will be able to see the number of wires your system has.

Elton20 09-11-2013 09:58 PM

Thanks guys
1 Attachment(s)
Here's the pic of my new thermostat

beenthere 09-12-2013 04:54 AM

Does everything work.

Brian28 09-14-2013 08:52 PM

I want to replace my Honeywell 5-2 thermostat with a Braeburn 5020, and use the 24v common option for power in lieu of batteries. Here's the problem: there is no C wire in the bundle at the thermostat. Down on the air handler control board, there is a white wire connected to the C terminal; this wire goes into a small separate sheath that also contains a red wire that is connected to the Y terminal, where it is screwed down together with the yellow AC wire; the separate sheath with the red and white wires goes to the condensing unit, according to the Bryant diagram.

So my question is, can I connect one of the unused wires in the sheath that goes from the control board to the t-stat to the C terminal on the control board, along withe the white condenser wire already there, and connect the onther end to the C terminal on the thermostat? Would this cause any problems?

beenthere 09-15-2013 03:24 AM

Tthats where it gets connected to. Won't cause any problems.

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