I have a 10 year old Carrier furnace. When in heat/ac mode the fan will work, but it won't run continuously in "on" mode. When the heat/ac is "off", and the fan is "on", it won't work at all. It used to work continuously when in "on" mode. The blower motor was replaced a few months ago and the problems started then. The LED light is not showing any problems. Is there a quick fix?