Hi I have a RHEEM FURNACE modal # RGDG-075AUER

The fan will not shut off, Even when I disconnect the thermostat.

I didn't see a fan controller except for the main board .

Call down to a rheem supply house give them the model number and ask if they had any warranty issues with the circuit board it might be the board sometimes they fail leaving the blower on letting you know there is a problem alsp see if it is pulling any codes hope it helps