Own a 90% efficient Bryant model # 398AAZ060100 Series A furnace. The other day I noticed the furnace was off and not calling for heat but the draft inducer fan was running. The only way to turn the draft inducer fan off is by the local disconnect. I replaced the pilot light assembly a few weeks ago and the main circuit board and transformer a couple of years ago. What is causing the fan to run constantly. Appreciate someone advising what is wrong and what part and part number to replace.
Thanks in advance for any assistance.