So the fan motor's 21VAC winding is working. That's good.
But either the fan blade is loose on the shaft (a super glue fix) or the fan motor itself had failed.You can find
helpful exploded view diagrams and order parts by entering your full
model number from the tag on the oven here.
The fan motor is shown on the diagram there as reference # 78, part # AP3192806, located behind the control panel and adjacent to the magnetron.
I'm not sure you have to pull the oven from the wall to replace it, but if you do, the oven installation (& removal) instructions are included on the tech sheet inside the unit.There
should be a "mini-manual" (tech sheet) hidden inside the unit
control panel, and it is very helpful when troubleshooting, testing, and locating
also download GE
owner's manuals and installation instructions here.
If you don't find yours I can send you a copy, or if you need more help, feel free to contact me directly (and please remind me of your
full model number from the tag on the unit).
happy to help you with free advice and we'd appreciate your
thoughtful rating of our answer.William E. "Ed" Miller,