I Want To Learn About Tstat Wires... - HVAC - DIY Chatroom Home Improvement Forum

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Old 12-06-2008, 10:06 PM   #1
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I want to learn about tstat wires...

This is just for knowlege becasue I'm curious...no particular problem to fix:

So I've spent the past two weeks trying to and sucessfully fixing my furnace but I have some nagging questions regarding the operation of the thermostat. Attached is a pic of how it is wired. I only have a gas furnace and no heatpump or ac or anything.

There are two wires a thin one and a thick one. One goes to my thermostat and the other goes to a mechanical dial thingamajig that lets me set the start time, length, and number of air cycles via metal plates. I do not know which wire goes to which but I suspect the thick wire with the yellow and blue not connected is the one going to the tstat.

I know a short between R and W on the control board initiates a call for heat, in this case from the tstat. There are other combinations like RG or GW shorts and others. What do these other combinations do?

What are the yellow and com terminals for and what other functions do you get?
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I want to learn about tstat wires...-wires.jpg  


thealexdexter is offline   Reply With Quote
Old 12-06-2008, 11:23 PM   #2
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R. 24 volt power supply out.
C. 24 volt common, A/C condenser common would connect here. Also common of thermostat if it needed a common.
W. Heat
Y. A/C, just a convience teminal on many older furnaces.
G. Fan


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