The exhaust fan thermostat is usually the failed component.
Exhaust fan on microwave won t shut off.
Thus turning the fan on will keep the electronic control board from getting too hot.
It cannot be turned off manually.
Microwave has automatic fan ignition setting pre programmed to keep the unit components from over heating.
When the microwave gets hot the thermostat closes.
The microwave has a base thermostat which is a safety device.
Fridgidaire microwave will not turn off check the fan.
When it cools down enough it will shut off.
It will come to help keep the controls cool inside the microwave control panel.
On several models of microwaves the thermostat is super sensitive causing the exhaust to run longer than needed.
The exhaust fan will turn on automatically during heavy use of the surface burners on the cook top if the fan thermostat senses too mush heat.
You might think that your microwave is still on because you can hear it running but what you are hearing.