Lennox GCS16-261-50-5P Rooftop

george7941

https://imgur.com/soTwbQB
The arrow shows a nipple on the outlet flange of the inducer fan whose purpose I do not understand. Is it to keep the fan in place if the mounting screws and nuts came loose?
The nipple gets in the way when taking the fan off or mounting it back on.
Also, there is a mounting plate for the outlet of the fan which has an aperture with an area less than half the area of the outlet of the fan. This restricts the exhaust gas flow. This square plate is on the outside with four holes through which screws are inserted and they go into the outlet flange. The cabinet wall gets sandwiched between this plate and the outlet flange. I do not have a photo of this plate but I can get one the next time I go back up on the roof. What is the purpose of restricting the flow?

Solid_Fuel_Man

I would guess the restrictor plate is calibrated to different burners. That way, the same ID fan can be used on multiple size units.

That square peg may just be an alignment dowel, but further investigation of if the port is open and if the pressure built by the ID fan goes through that port to something like a proving switch or something.

george7941

I will check into the hole in the peg the next time I go up on the roof. It is definitely not connected to any switch or sensor since there are no switches or sensors on the fan unit and there are no extra ports at the fan inlet.

Solid_Fuel_Man

If that were the case, and it impeded removal or re-assembly it would go away if I were around. Man, I despise rooftops!

george7941

Exactly the way I feel about the peg. If I ever take the fan off again I will grind down most of the peg.