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 Y1 and Y2 - AC & Furnace
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Posted - 07/27/2017 :  02:00:35 AM  Show Profile  Visit tadejm's Homepage  Reply with Quote

I have an Ecobee EMS Si thermostat. In regards to wires. How is it possible run AC and Furnace on Y1 and the same for Y2? second stage. how do the outputs on AC and Furnace look and what is their voltage?


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Posted - 07/27/2017 :  03:05:44 AM  Show Profile  Reply with Quote
We need you to provide more information on what you want to control.
Like HVAC model or control board.

What terminals on the original thermostat are now connected.
Make notes of the wire colors on the original.

There are many ways they can be wired for control. Depending on the system.

Your manual should give you some ideas. It has many different configurations depending on what you have to control.

Some automatically control the Fan when either heat or cooling is requested. Others us the separate G Fan output on the thermostat to start the Fan.

Some use a separate 24VAC transformer for cooling and another for heating.
While some have one 24VAC transformer and RC and RH terminals are jumped in the thermostat.

Edited by - BLH on 07/27/2017 05:23:24 AM
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Advanced Member

15854 Posts

Posted - 07/27/2017 :  1:13:58 PM  Show Profile  Visit stusviews's Homepage  Reply with Quote
Y is for the AC, W is for heating. The Ecobee EMS Si thermostat already has a Y1 and Y2 terminal for 2-stage cooling. The thermostat also has W1 and W2 in the event that you have 2-stage cooling.

Standard thermostat voltage is 24VAC.

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Advanced Member

812 Posts

Posted - 07/29/2017 :  05:16:25 AM  Show Profile  Reply with Quote
In general, if you have just a single stage AC and a single stage furnace, you use Y1 or W1 respectively, ignoring Y2 and W2. All thermostats I've seen allow you to short the second and the first stages, but it shouldn't be necessary. At any rate, consult your manual. It all should be there.

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