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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8327
Experience:  Furnace, A/C and heat pump specialist.
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My lenox 80MGF3 75 A6 FURNACE exhaust blower and igniter

Customer Question

My lenox 80MGF3 75 A6 FURNACE exhaust blower and igniter continue to cycle until lockout even when the thermostat isn't calling for heat. How do I fix this issue? Is it a welded relay contact?
Submitted: 2 years ago.
Category: HVAC
Customer: replied 2 years ago.
It has a RAM 3mc5 pc board.
Expert:  airheatman replied 2 years ago.

Turn power off to reset board. The turn power back on. Let me know if you get an error code immediately and if so, what the code is the very first time furnace attempts to light.

Customer: replied 2 years ago.
I don't get any error codes until it locks out. Then it is the 2 flash code.
Customer: replied 2 years ago.
When the thermostat is set to heat it is giving the fast fash code.
Expert:  airheatman replied 2 years ago.

OK if you are getting inducer come on with no call for heat issue is going to be an open limit or defective board.

However we should get an open limit code on first attempt.I would start by just making 100 per cent sure the limits are closed and if so replace board.

I am showing Lennox part number to be 33J6201

The upgraded board shows to be a Part Number:19W94

See link below and verify that is the correct board: