Lennox 80MGF4/5-120A-7 furnace - blower and burners stop at the same time

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Old 01-01-16, 01:54 PM
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Question Lennox 80MGF4/5-120A-7 furnace - blower and burners stop at the same time

I have noticed for about a month that my blower and burners stop at the same time at the end of the heating cycle. Blower kind of skips the cooldown of heat exchanger for expected 180 seconds after burners stop. It seems that the expected blower cooling cycle kind of starts at the beginning of the next heating cycle. New heating cycle starts with 30 sec of blower, then it stops and the normal procedure starts - inducer-burners-blower but again finishes kind of abruptly with both burner and blower stop simultaneously when heat demand is met. Furnace is working good, heats to needed temperature, integrated control board's 2 diagnostic LEDs are flashing green slow and simultaneously stating "operation normal" - a bit faster flashing when furnace is in operation meeting heat demand.
Concerned about the heat exchanger is not being cooled down appropriately at the end of the heat cycle and will eventually crack or else.
Furnace installed in 1998 and never had any issues. Never had professional service but have cleaned it myself regularly and carefully according to internet instructions. Could a couple of power outages about one month ago caused it to "get confused"?
 
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Old 01-01-16, 02:37 PM
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Little confused, but inducer motor will stop 5 sec after the stat is satisfied. The blower will continue to run for at lest 90 sec. Depending on what control they installed in the furnace.
 
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Old 01-01-16, 03:06 PM
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Welcome to the forums.

From the information I've found.... your blower operation is controlled strictly by the control board.

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It would appear that the blower timing section on your control board is defective necessitating a board replacement.
 
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