Chosen Solution

Kenmore Microwave model 401.8504*,85143 Whenever door is opened the fan (I think it’s the fan) is running

Bad sensor/switch within the microwave. Latch body and switch assy. part number DE96-00414A needs replaced. The latch body and switch assembly DE96-00414A comes with the switches that monitor the door position and the latch body that holds the switches in place so the switch is bad causing the unit to not detect the stopped state.

You have a bad door switch. here’s a video on how to fix it: https://www.youtube.com/watch?v=S0aqo9sM