Fan does not shut off - Whirlpool MH3184XP Microwave Oven

Yes. Faulty door interlock switches.
Replace the door switches with the correct ones.

What is the make/model? Are you sure you didn't turn on the VENT FAN? Need more info....

Can you hear the "whirl" of the fan? It is possible the fan is not turning & cooling the oven therefore it will shut down when it reaches a certain temperature. This could be caused by a supply fault to the fan or the fan motor, either way it would need to be tested by a qulified engineer.

some switches are normally closed "short position" press switch "open" it will be labeled NC on the one side, "stands for normally closed" and others will be NO "stands for normally open" press switch "short" if there is no change in readings when you press switch it is defective.

I would check the door switches for a faulty switch. If it were condensation on the control panel. I would think it would have dried out by now unless it has damaged the control board.

The internal cooling fan (blower) is faulty and will need replacing.

May be a sensor or thermostat for the fan thats faulty therefore it runs all the time.

My Kenmore microwave oven fan has been turning on and off, almost every hour. Sometimes 3 or 4 times in one hour. It's very random. Model No. 721-80593401 Serial No.503TA03208
Please help!!!

A little late for a reply; you probably have replaced it by now.

I suspect it shuts down because the fan is no longer turning on and there is probably a thermal shutoff switch near or on the magnetron to prevent the chance of fire.