I've done the self test and and also put the furnace into "fan on" (i.e. not auto) mode, and in both cases I can hear the relay click but the blower does not come on. What would be my next troubleshooting steps?

My setup also has a Honeywell electric air cleaner upstream of the furnace, the status light for which does not come on. Is it possible that malfunctioning of this unit would cause the blower in the furnace to keep from coming on?