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airheatman
airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 7747
Experience:  Furnace, A/C and heat pump specialist.
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Have a G61MP Lennox furnace and I think the control board

Customer Question

Hi, have a G61MP Lennox furnace and I think the control board (46m9901) is faulty
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

Give me a few more details as to what is happening and how you have diagnosed issue to be with board.

Customer: replied 1 year ago.
the fan is constantly blowing, with no heat. It happened two times recently. each time I turned off the furnace and after few hours I tuned it back on, and it started to work properly again.
Customer: replied 1 year ago.
I mean each time I shut off the main power from the furnace room.
Expert:  airheatman replied 1 year ago.

Let me ask you this. When blower runs but fails to provide heat, do you get an error code on the board ?

Expert:  airheatman replied 1 year ago.

Turning power off and back on resets any error codes until the issue happens again. For example if the pressure switch opened prematurely we would get 2 blinks followed by 4 blinks on the led on board

Customer: replied 1 year ago.
there are two LEDs on the board. when it blows with no heat they are both off. but when it is working fine both LEDs are in simultaneous slow flashing mode.
Customer: replied 1 year ago.
turning the power off and back on does not bring it to normal operation. I do it multiple times, and wait long in between .
Expert:  airheatman replied 1 year ago.

Ok when power is on to furnace but no call for heat we should have a 1/4 second flash followed by 4 seconds off.

On call for heat, the lights should be a constant 1/2 second bright followed by 1/2 second dim the entire heat cycle unless something fails. If it fails we should get a code determined by blinking lights.

If we are getting no lights when it fails and if it does not reset immediately upon restoring power , the it definitely seems board is failing.

Customer: replied 1 year ago.
we are getting no lights when it fails and it does not reset immediately upon restoring power.
Expert:  airheatman replied 1 year ago.

Is this something you are wanting to find online and replace yourself or are just verifying the diagnosis? If you are wanting to replace yourself, look on board for a number like 63W57 or similar and I will assist you in locating.

Customer: replied 1 year ago.
right i am trying to find a replacement, but look like 46m9901 board is no longer available
Expert:  airheatman replied 1 year ago.

Can you provide the rest of the numbers in model after the G61MP?

Customer: replied 1 year ago.
G61MP-60C-110-01
Expert:  airheatman replied 1 year ago.

Take a look at this board and see if has all the terminals yours has.I a showing available from AC Parts direct:

https://acpartsdistributors.com/index.php?main_page=product_info&products_id=4900

Expert:  airheatman replied 1 year ago.

I am showing OEM part was 86W81.

All parts also has it listed.Click this link and scroll down .You will find it listed by part you gave me on left side of page

http://www.allpartsheating.com/lennoxcircuitboards.html

Customer: replied 1 year ago.
the first link you sent has different image and it does not match with my board.
the second link you sent I can't enlarge the image.
Here I found my board offered by this website http://awesomesurplus.com/order/43 ($150); but I don't know this website.
Customer: replied 1 year ago.
I got the picture for 86w81 here: http://hvacpartsandmore.com/index.php/86w81-607845-03-ignition-control-kit.html
the board terminals do not match with my board.
Expert:  airheatman replied 1 year ago.

I have not heard of the website either,I think I would trust one of the ebay sellers with high feedback before a surplus site.Didyou look at some on Ebay yet?

Customer: replied 1 year ago.
i searched ebay, but nothing is currently available.
Customer: replied 1 year ago.
yeah I saw 21M51U-843. it is available on amazon for $159.01 + $4.99 shipping . the problem with this is that it comes with a new ignitor that works with a different voltage provided with the new board. So my existing ignitor won't work with this board. I have to modify my unit and make a bigger hole to install the new ignitor, which I am trying to avoid and see I can still find the original board.
Expert:  airheatman replied 1 year ago.

It appears the old board has been discontinued. Even from the Lennox parts store (which I don't usually recommend due to pricing), is showing the board has been replaced with that upgrade kit.The only way you may find the old board would be to find a used one on an old unit somewhere.

Customer: replied 1 year ago.
I went down to furnace room and turn it back on and now it is working fine again. wondering what can cause the board being faulty like that. is there anything I should check to see if I can avoid this happening again? Is a surge protector recommended? Can the thermostat be the issue?
Expert:  airheatman replied 1 year ago.

Thermostat would not make the lights go off on board..If thermostat were failing to send signal, the lights would go back to the pulse (no call for heat).

You might check power wires and ground to be sure they are secure. Erratic behavior is common for a failing board.

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