GE JVM1640WB The fan will turn on when the door is open. Whether the microwave cycle is done or not. Has done it intermittently for a awhile. It still cooks OK but once the tim er goes off and you open the door the fan comes on.

Your primary interlock (bottom door switch) is probably shorted, or its mount is damaged or misaligned, keeping it in the "on" position.

Even though a door switch clicks, it may still be bad inside.

Door switch or mount trouble is usually caused by slamming the door or by opening the door while it's cooking without hitting the Stop pad first.

There are plastic mounts inside the microwave which hold the door switches and onto which the door latches lock when you close the door.

The screws on these mounts may be loose. If they get too loose, the switches will not be activated properly.

Sometimes it's a broken tab on the switch holder, allowing the switch to rotate just out of position. This tab can be hard to see, since it is under the bottom edge of the switch.

If you or someone you know decide to look into it, we have critical information on safety, disassembly and door switches at our site, and our link is at our listing here on FixYa:.

You can find helpful exploded view diagrams and order parts by entering your full model number here.

There should also be a "mini-manual" hidden inside the unit behind the control panel or hidden on the left side behind the grille, which is very helpful when troubleshooting & testing.

At our Web site, we have a video available showing how to remove a typical over the range control panel assembly in under 5 minutes.

If you only need a switch, you can order a universal type here for $5 postpaid.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.