I am attempting to replace my current thermostat (mercury type) with a White-Rodgers 1f82-261. The current stat is wired with 4 wires; red->'r', green->'g', yellow->'y' and orange->'o'. The new stat requires 24v power from the system which means I need to get the common side of the trans back to the stat. The cable at the wall has 7 wires in it. When I put a meter on the red and blue wires I show 24vac. I opened the panel on the heatpump (Heil) and the blue wire is not connected to anything so I'm left wondering how the circuit is being completed.
Do the control wires typically connect to something else (transformer?) between the heatpump and thermostat? I had assumed the transformer is located within the heatpump and the 24vac is supplied via the red wire to the stat which then determines which path it returns on. Is that correct? If so, I was thinking I could just connect the common side of the transformer to the blue wire and violla. Since I'm already showing a circuit with the blue and red, and the blue is not connected at the heatpump side, I'm stumped.
Any help is appreciated!