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I wanted to get a programmable thermostat, but when I look at the wiring of the existing thermostat I’m not sure why the white and orange wires are both going to the W terminal. enter image description here

Other thermostat wiring, located downstairs second thermostat


At the zone board there are 3 orange wires plugged into it and one that isn’t plugged into anything. There is an orange wire in the first terminal of the HP and Duct area under the sensors section. There is also an orange wire plugged into the O terminal under equipment. I made a black mark on this diagram to show where orange wires are connected.

Zone controller orange wire locaiton

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    Can you show us the wiring at the furnace? Do you have a humidifier? – Tester101 Dec 3 '17 at 22:02
  • No, I have a heat pump. It goes to zone board, I’ll see if I can get a clear image. This is the zone board i believe,link – anthonyjhd Dec 3 '17 at 22:25
  • since it's a heat pump, I agree with Ken. They are using the W terminal from the thermostat, to activate the reversing valve. At the zone controller, is the orange thermostat wire connected to the B terminal? – Tester101 Dec 4 '17 at 12:42
  • You don't know which of the orange wires is from the thermostat in the photo? – Tester101 Dec 4 '17 at 19:14
  • Not yet. I have a friend brining a some kind of tool that can do that later on. If the situation you described earlier were the case, would leaving the orange wire unconnected prevent heat from working? – anthonyjhd Dec 4 '17 at 19:32
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Your Existing Thermostat may not have been the proper thermostat for your unit. However it was made to work - utilizing a wiring trick.

The below is a rough guide for AC thermostat wiring.

Orange wire and Blue wire are usually a reversing valve.

RED, RED[c], RED[h] is 24VAC where c stands for cool and h stands for Heat.

W or W1 White (Heat Stage 1) , W2 [color can vary] (Heat Stage 2)

Y or Y1 Yellow (Cool Stage 1), Y2 [color can vary] (Cool Stage 2)

G Green - Indoor Fan (Evaporator Fan - Blower inside house)

E - Emergency Heat

Basic Thermostat Wiring

EDIT 12/05/2017

I am guessing that the outside units are different model units - but it does not matter.

I am thinking that the orange wire might be the loose one on the other side. To know for sure - we already know that the orange and white are tied together on the thermostat side - so it forms a continuous run of wire (continuity) - measuring on the other end of those wires for continuity - we should see it as ONE wire and not two. So on our zone board side we take a continuity tester or better an Ohm Meter; you can get a cheap one for about $5-$10 . With your Circuit breaker off perform the following.

At your Zone Controller where the white wire from your thermostat unit should come in as W1 (disconnect it ) and Measure ohms between that white wire and each of the orange wires - one of them should show continuity if that Orange wire is any of those that feed to the zone board. This is how you can determine which Orange Wire is the wire form that thermostat - your meter should read less than about 3 ohms. You can then LABEL that Orange wire as Your Thermostat #1 or #2 which ever one it is and then report your findings back here.

  • At the zone board there are 3 orange wires plugged into it and one that isn’t plugged into anything. There is an orange wire in the first terminal of the HP and Duct area under the sensors section. There is also an orange wire plugged into the O terminal under equipment. I made a black mark on this diagram to show where orange wires are connected. link – anthonyjhd Dec 4 '17 at 18:56
  • @anthonyjhd - the O line on equipment - does it go to the equipment? Is it contained in the same wire jacket that goes to the equipment ? Take a picture of your connections in the box. Also your other thermostat. Doe sit have the same configuration ? It could be they are powering a duct open or closed using the orange wire from the thermostat at W1. But why connect it there does not make sense when a jumper directly on the zone controller would do the same thing and be easy to know what was done and why. – Ken Dec 5 '17 at 1:47
  • i added an image of the other thermostat. Its difficult to get an image of the zone board. – anthonyjhd Dec 5 '17 at 17:54
  • @anthonyjhd - If you can't get a good pic of your zone board - can you label the diagram or make a chart of wire color, what system/device it goes to (wire jacket) and where on the zone board it is connected to. I will add an edit on my answer in about 10 minutes. – Ken Dec 5 '17 at 23:27
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    I had someone loan me a toner and confirmed that the loose wire was the one attached to the thermostat. – anthonyjhd Dec 6 '17 at 2:22

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