If W1 and W2 are jumpered, the furnace will start the heat cycle on low
stage heat and will automatically kick up to high after a certain time--
I think about 7 minutes. A/C will not be affected. If there is any way
to run new wires, do so. If it is absolutely impossible to get wires
through the walls without tearing drywall up, see if there is any other
location to put the thermostat. If you are going to go to the trouble of
running wire, run 9 conductor wire for any future needs. Good luck!