I have an airquest furnace. It had a 2 wire thermostat and I changed it to a 3 wire so I could run the fan continuously. The fan will come on if I keep tripping the safety switch on the blower motor compartment door but then will quit after a few minutes. It also does this even if the thermostat is in the auto mode. The red, green and white wires all are in the right spots. I can also hear a faint hum when the safety switch is engaged but the fan does not come on. Then after several times of pushing in the safety switch, the fan will engage. Once again, this happens even if the thermostat is set to auto. I have seen some of your posts and I like the way that you respond to people that ask questions. The furnace fan does work in the heating mode. Any help would be appreciated. Thanks in advance.