I had a complete new HVAC system installed for the downstairs portion of my house. The installation required a new t-stat since it is a 2-stage cooling system.
I really like the features on the new t-stat, and purchased one for my slightly older 1-stage upstairs HVAC system as well. One of the features I like is that it runs on household power, using the batteries for a backup. It's my understanding that I've already basically got power to the t-stat via the R wires, and that I just need to add the common to basically complete the circuit.
I looked at the wiring to the internal board, and there is a wire running to the common, which runs to a "safe-t-switch," and then continues on to somewhere I can't locate. There is a separate bundle of wires that runs to the t-stat. Can I use one of the unused wires in this bundle and ALSO connect it to the common on the board, or will that mess up the "safe-t-switch?"
System is a Frigidaire with the following model numbers:
Wires leaving furnace:
Old t-stat connections (was an old Hunter t-stat):