I just installed a nest thermostat. The previous thermostat did not have a C wire attached. It G, RC, (RH Jumper), Y and W. When I hooked up the nest thermostat it was short cycling the blower fan until I pulled the AC (Y) wire.
I've been reading this happens if there is no C wire then the nest is trying to draw power from the furnace.
I then tried to attach the blue wire which was unused in the previous thermostat to the nest C terminal. The nest threw an error saying it was not getting power from this wire.
This isn't an ideal situation because once summer comes i cannot use my AC. I'm looking at my furnace and looks like the C terminal is connected but that wire is also joined on the Y terminal? I attached a picture of the furnace wire configuration.
Wondering if there's something I can do here to give the blue C wire power at the thermostat or if I should go with the venstar add-a-wire?
Old thermostat wiring: