I am in the process of upgrading my circa 1990 thermostat (4 wire) to a T6 pro. We have a First Company 30HBXB-HW hydro-air system with control board model CB201V. I need to upgrade from 4 to 5 wire. I’ve attached an image of the wiring diagram. Can I just tie in an additional wire to one of the “COM” lines (before it goes to the condenser) and bring that to the T6 as a common (red dotted line in the diagram)? Thanks.
Yes you can.
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