(Please Help) Lennox g20q3/4e-100 damper motor replacement?

digitalis

I recently had to replace a blower motor from my old Lennox G20 furnace. The unit, while old, was still in great shape. Sadly the tech that was sent to replace it was not familiar with it and forced the damper door close a few times, breaking the delicate damper motor.

The unit was working when he left but the damper door was doing a clicking noise as if the motor was skipping or not catching a gear. He said it would be fine but that he would help me find a replacement.

Now after a couple of days, the damper door is not able to open the clicking noise still indicates an issue with the motor. The furnace stopped working and the tech is MIA not returning my calls.

Is there any way to bypass the motor and force the damper into an open position while I find a replacement online?

The guy seemed fresh out of school and I even had to help him with the replacement of the blower motor and wiring. I have an electronics background and build computers from scratch so I'm quite certain I can replace the motor when I locate a decently priced replacement but I would love to know if there is a way to safely bypass this system until then since we are already dropping below the 30s

Thanks for any helps or suggestions you may provide

EdTheHeaterMan

There is an end switch that proves the damper door is open. If the door was to be propped open permanently with a metal rod or bracket, the end switch may connect.

Otherwize, remove the damper completely and connect the end switch wires with a wire nut.
DO NOT WIRE NUT THE END SWITCH WIRES TOGETHER WITH THE DAMPER IN PLACE
Can you take a picture of the wiring diagram on the blower door and post it?

EdTheHeaterMan

Found it:
look at the damper detail. The prover switch is located on the left side of the damper box. If you can get a metal strap and keep that damper open permanently the switch should be activated and the burner should operate.

digitalis

This is great, I was able to get it going!!! Thank you so much! you are a lifesaver. Now if anyone knows a good place online to order the right parts for replacement let me know.

ayrtons2k

Hi Digitalis,

I'm having the same problem and was wondering:

1. Did you replace the replace the damper motor?
3. Did that solve the problem?
2. How much did it cost and where did you buy it from?
4. Can you please share your experience with the replacement procedure (pitfalls, recommendations)?

For anyone wondering, the part number for the motor is: MOTOR-DAMPER 51H7401 "110V,1 RPM
This is the least expensive price I've found (as of this post it was $207):
https://www.supplyhouse.com/Lennox-51H74-110v-Damper-Door-Motor-1-RPM


Thanks in advance!

EBEBRATT-Ed

@ayrtons2k

Your better off starting a new post