Microwave has automatic fan ignition setting pre programmed to keep the unit components from over heating.
Exhaust fan on microwave won t shut off.
When it cools down enough it will shut off.
The exhaust fan thermostat is usually the failed component.
It will come to help keep the controls cool inside the microwave control panel.
If you are cooking on the cooktop it can sense the heat and the fan won t turn off until the thermostat cools.
It cannot be turned off manually.
When it senses heat it turns on the exhaust fan.
The microwave has a base thermostat which is a safety device.
Thus turning the fan on will keep the electronic control board from getting too hot.
When the microwave gets hot the thermostat closes.
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.