Originally Posted by brutis
Not sure, how would I be able to tell if that is happening?
Generally there would be a second unit nearby. You could also have a two stage heat pump.
If you feel comfortable with this you can open the side of the heat exchanger and see if that wire is connected to anything. Just use the color code.
It could be that the wire is just connected at the thermostat and not connected at the other end. I have seen that in the past.
A customer converts to a heat pump and the thermostat is never checked. They just hook up the wires that need to be hooked up to the unit to get it working.
Lazy, yes. Does it happen? More that one would think. When it comes to wiring of any kind I am never surprised about anything I find.
Although I must say that I have not seen anything weird in the last few years.