The fan on my warn air furnace cuts on and off regardless of the functioning of the unit. In other words if the gas is off the fan will come on for no reason (well it's doing it for a reason but I don't know why). Also when the gas is on the unit is running normally the fan will cut off for a minute or so abd then turn back on. I know this is not normal operation. The fan limit switch was replaced recently and the unit has been running this way every since. From reading some of the questions and answers I think this may be the problem. If this does not sound like the problem to you please recommend something else.

Adjust in small increments.