I just bought a house with a 1983 heatpump and furnace system. The heat pump has had it and isn't worth fixing. Some previous owner had it diconnected from the control system. I just use the furnace to heat. Problem is, that the system starts the furnace fan hoping for heat from the now-disconnected pump, but doesn't get it. The furnace finally kicks in, and then the fan runs for a long time after the furnace shuts off once the set temp has been reached. How do I rewire to get the fan working only when the furnace is on??