thermostatthermostat-c-wire
I am planning on installing a new WIFI thermostat (Honeywell RTH6580WF). I have a heat pump system (outdoor condenser unit and air handler in attic). Old thermostat did not have a 'c' wire, but it does have an extra wire in the bundle that I can use.
Do I need to connect the new 'c' wire on both units? Or will hooking the one to the air handler be enough?
First off, the green wire should connect to the G terminal on the thermostat. It's connected to the G terminal in the furnace, and so should also go to the G terminal on the thermostat.
At the thermostat, the extra blue wire should connect to the C terminal. Depending on the furnace (read the documentation, and analyze the schematic to be sure), you should be able to connect the other end of the blue wire to either of the C terminals in the furnace.
According to the schematic, the B terminal does appear to be connected to the transformer.
I'd actually trace the wiring in the unit just to confirm, but based on the schematic it looks good.
You'll want to make sure the transformer has enough power to supply the additional load of the new thermostat, but typically it isn't a problem. If you hook up the new thermostat, and the fuse inside the unit blows. That would be an indicator that the thermostat is drawing too much juice.
Best Answer
You should connect the
Cwire, from whichever unit supplies theRwire. Typically it's the air handler, but since you've given no details it's impossible to say for sure.