Originally Posted by avxflyer
I'm trying to run the fan on my furnace and it's not working. The heat and AC work fine and the fan turns on with those options, but not when I simply turn the fan on. I jumpered the G and R wires at the thermostat, but still nothing. Then I jumpered the G and R on the control board and there is a click. I'm assuming this is a relay. The fan still doesn't start. I had the whole control board replaced about a year ago, but never tried the fan on its own. The furnace is a Lennox about 13 years old. The control board has a flashing red and flashing green light. Both are flashing at the same time. Not sure if this is normal or indicates a fault. Any insight on what is going on?
When you jump G and R on the board, the board should start the blower.
Check the wiring on the board, one blower wire on the heat post, one blower wire on the cool post. Do you have a post marked const. blower?
Usually this is done through the stat. Some furnace's the fan on is cool speed and some it the heating speed. Paul