This is not a heat pump system, just forced air gas. I've noticed that the wires hooked up to the thermostat and then reappearing at the furnace don't match. On the thermostat there is an unattached blue wire, and attached white, yellow, green and red all attached to the correct terminals.
At the furnace, the thermostat wires are red attached to red, black attached to Y/Y2, white attached to W/W1, blue attached to green, orange attached to nothing.
I noticed that the green wire does not come from the tstat wires, it's in a separate bunch of wires of all colours. However, it's connected to the G terminal and there's another connection to the fan (a plug that you can pull in and out to different fan levels). Then the whole bunch leads back to the blower at the back of the furnace.
This is getting more and more complicated I think. Thanks for your help!