Original post by: j.eldon ,
I just swapped out the bottom switch of our GE microwave oven because the fan ran with the door open. The switch does ring out OK on an ohm meter, but the return spring seems weak, and it does not click positively and resoundingly the way the new replacement part does. I suspect the old switch is unable to lift the plastic piece the door engages, and thus stays down in its electrically closed orientation, signalling that the door itself is closed. Anyway, the new one ($8 for two on eBay) fixed the problem quickly.