Bad control board or something more nefarious?

Old 02-09-20, 06:14 PM
Thread Starter
Join Date: Jun 2019
Posts: 3
Upvotes: 0
Received 0 Upvotes on 0 Posts
Bad control board or something more nefarious?

Dear Experts:

My thermostat was sending the signal for cooling but my AC wasn't kicking on (neither the blower nor the AC unit outside). Upon checking the control board in the furnace, I found out that the unit was getting power, but the LED lights on control board werenít lighting up. I turned the power switch off and on a few times and the first couple of times, the LEDs on the board lit up but then quickly went out with a faint crackling/fizzling sound. This only happened a few times. Further attempts at flipping the power switch off and then back on failed to produce any signs of life. Upon closer inspection, it looks like one of the capacitors is fried. My concern is, is that bound to happen with these boards over time? Or what else could have caused the issue? Also, to give some background, in August 2016 we had to replace the fan blower motor and capacitor and just a few months ago in November 2019 we had to again replace the capacitor for the blower motor. Iím sharing this info about the other repairs in case it paints a picture of something systemically wrong with my system, or if those repairs (and frequency of them) are common.

I donít want to replace the board only to have something weird with my electrical wiring that will fry the new one also. I have lived in this house for 6.5 years and have never replaced the control board and I think the control board itself is dated 1996. Is 24 years a good run for a furnace control board or should I be investigating other issues? Can anyone tell me how to find the exact model number that I would need to order in order to replace the control board myself? Or tell me how to find out? Itís a Lennox furnace and here are some pics of the board and the wiring diagram.

Thanks in advance for your time and your advice.


Attached Images     
Old 02-09-20, 08:35 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,100
Received 3,982 Upvotes on 3,574 Posts
In the picture it does look like the board is damaged.
Could be a capacitor or diode failure. Is it common..... not really.

To order a new board you will need the full model number from the ID tag inside on the side wall near the burner. Write the serial number down also.

Your current board should also have a part number on it. Usually near one of the corners.
Old 02-10-20, 08:31 AM
Geochurchi's Avatar
Join Date: Nov 2012
Posts: 5,082
Received 161 Upvotes on 147 Posts
Hi, you could lift the board out and check underneath for bad solder joints, but a board that old could be gone.
Old 02-10-20, 04:33 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: Jersey
Posts: 65,100
Received 3,982 Upvotes on 3,574 Posts
A definite problem on the board................
Name:  pcb.jpg
Views: 89
Size:  28.5 KB

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: