Hi! I am having some issues with my furnace blower.

1) Fan is on "Auto"
2) Thermostat calls for heat
3) Green light comes "On" on IPI module and then burner comes "On"
4) Flame occurs
5) Blower doesn't come "On". After a while, the burner stops for safety reasons. This issue repeats until the thermostat blower switch is flipped to "On".
6) When the burner is "On", I switch the blower to "On" and the furnace keeps running until it meets the thermostat setpoint. Then the burner shuts off, but the blower keeps running, because it's on "On" until I turn it off.

Is there some sort of sensor that needs to be replaced? Is it easy enough for me to fix?

Thank you in advance for your assistance.

Mark

You have 2 different speeds for the blower motor. The fan on uses a different winding and relay for on than auto. Likely the auto relay is bad, although it could be a problem with the motor windings. If you are not getting power to the blower in auto, it is the relay. Unfortunately, that usually means a new control board.