These units run just like a furnace. The burner fires up and heats up the combustion chamber where the fan switch is located. When the fan switch’s predetermined temperature is reached it turns on the blower fan. If the blower fan comes on right away then more then likely the contacts in the fan switch are welded together from arching. Also on the newer model there was a relay in the junction box where the contacts would weld together from arching off and on.
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