Maytag only heats if vent is on

I live in rural Alaska with the nearest repairman a $300 flight away. My over the range microwave suddenly quit heating. The light, vent, timer, and control panel all work. The turn-table spins and everything looks and sounds like normal but the microwave doesn’t heat. After reading different forums, someone mentioned that their microwave would only heat if the vent was turned on low. I tried that and if I turn the vent on, the microwave does heat. This seems to me only a temporary fix. Does anyone have any advice as to what could be wrong and if it can be fixed by a layman? Do I need a new microwave? I obviously hope that it’s a cheap and easy fix but I can’t live without my microwave. Thanks for any help!