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Old 05-21-2015, 09:46 PM   #1
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Thermostat wiring

I have novice electrical experience, but I'm unfamiliar with HVAC setups. Last year I purchased a new thermostat for an older house, but I'm only now getting around to hooking it up. As best as I can tell one of the previous owners had a unit that was 5-wire, but the current unit is only four:

I've confirmed all five wires (blue, yellow, green, red, and white) feed through the house and to the thermostat - except the blue. It's not connected at the unit or the current thermostat. Here's the diagram for the unit:

The thermostat is a Insteon 2441TH, which uses five wires (I believe I'm only missing the Common). I also have a Venstar Add-A-Wire, but I'm not sure how to wire it up (if it is even needed). All the Venstar examples refer to wire colors or designations that aren't obvious in this setup. I'm stumped with what I need to wire together; any help with what I actually need to connect would be appreciated.


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Old 05-21-2015, 10:19 PM   #2
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Thermostat wiring

If you need a common just hook the blue to a convenient spot on the 24 volt side of the transformer. That would be the lower right part of the transformer in the diagram. Gray or black wires.


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Old 05-24-2015, 03:07 PM   #3
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Thermostat wiring

You have to connect the blue to the 24 VAC sise of the reansformer that is opposite polarity to that qwhich is connected to the red wire going to the tstat .

God bless
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