Furnace was giving a limit switch open code.

Blower motor isn't being called for by controller board, no 120 VAC coming out of the controller.

I've bypassed the controller board and ran 120 VAC right to the blower motor "heat" wiring.

Question #1 - I know some folks leave the fan on continuously, but we never have. Is this hard on the fan? Part of me says yeah its constant use so it must be, but the other part thinks the start/stop is probably harder on it.

Furnace is a Lennox G50UH-36B-090-06 with a 97L4801 White-Rodgers controller board.

I can get the same model board from Amazon and others, but it looks like the connections have changed on it. It also won't arrive until next week.

I have a local place that when I search returns this board. Model 19V36, saying it has replaced 97L48. It looks very different and comes with a few extra wiring harnesses, and what looks like a flame sensor, but different than my unit's flame sensor.

Question #2 - Any of you HVAC guys have experience replacing this board? Am I better off waiting till next week for the same model rather than trying to replace with the other one?

Question #3 - If I wait until next week for the replacement can I leave the fan on continuous that long or should I just run the heat when I need to, to warm the house up a bit, then shut it down?

Question #4 - Should I just call an HVAC guy and let him source a board and replace it?

Question #5 - We know we're getting close to putting a new furnace in. Should I just bite the bullet and do it now?

Run the blower constantly until you get the new board.
Just make sure to unhook the motor wire from the cooling tap. In case you have to use your air conditioner (unlikely this time of year in MI).
Otherwise, you'll have two motor taps energized and burn up the motor.

Here's the replacement board you need. Manufactured by the company who made the OEM board.
https://www.supplyhouse.com/Wh...-Furnace-Control-Kit

If you look in the documents under 'manuals', then the 'product overview', you'll see the above board replaces your original board.

quote:

Originally posted by Excam_Man:
Run the blower constantly until you get the new board.
Just make sure to unhook the motor wire from the cooling tap. In case you have to use your air conditioner (unlikely this time of year in MI).
Otherwise, you'll have two motor taps energized and burn up the motor.

Here's the replacement board you need. Manufactured by the company who made the OEM board.
https://www.supplyhouse.com/Wh...-Furnace-Control-Kit

If you look in the documents under 'manuals', then the 'product overview', you'll see the above board replaces your original board.

Thank a ton Excam_man. Somehow I came upon that board last night during my searches as I still have a browser window open with it. I wasn't sure if it was the same or not though. Not sure how I stumbled across it. I think it might have been through Grainger's site as they listed alternate boards by original board number.

Looks like they stock that board at the local place here called Repair Clinic, but it didn't come up in my search there by model number. I'll get it ordered, go pick it up and hopefully we'll have normal operation later today.

I'll keep you posted, and thank you again!

Another big thanks to Excam_man for the tip on that controller.

Strange that it didn't come up as a replacement when I was just "googling", and stranger still that it didn't come up from RepairClinic.com as they're usually pretty on the ball.

It was a great fit, and had good clear instructions on the adapter harnesses.

Only issue was that whoever installed the humidifier didn't leave enough extra wire to reach the new pin, but I fashioned a jumper and it should be good to go.

Your very welcome.
Happy to see ya got it back up and running properly.
Always nice to see a positive outcome!

Great news ... ! Went through a similar problem so understand.