About a week ago I went to use my over-the-range Maytag microwave and found the cooling fan (not exhaust) would come on when the door was opened. I mentioned it to my wife and she said that she noticed it as well so naturally I blamed her for breaking it.
I installed this microwave in 2009 and I suspect it is made by Whirlpool so is a common design. Thinking that the control board was shot and it would have to be replaced I did quick search on the symptom and found a YouTube video explaining how to access suspect microswitches.
A few screws, Phillips and #20 Torx I opened up the control area and found a service paper with location and the logic of the door switches. There are two screws on the top to remove a trim piece and a screw at the top and one at the bottom of the control panel to allow the control board to swing out from the top. This allows access to the three interlock switches, one the upper latch and two on the bottom. The service paper identified two NO switches and one NC. A quick check with a meter found a bad switch and two days later Amazon delivered a replacement to fix the situation. The piece holding the switches is held on by two #20 Torx and then has two clips holding it to the chassis.
Some images that may help someone with a similar problem.
