This is a countertop microwave.

When I press the button to open the door, the fan started to turn on and it keeps on until I close the door. Microwave is still heating fine.

Is there a way to fix it?

Thanks for your help.

Cool, thanks. That is what I was thinking last night.

As an update. I fixed it.

Turns out the Primary Interlock Switch (bottom location) is bad. It is a 15A NO microswitch.

There is a mistake in the part list in the diagram in: Replacement parts for General Electric JE1425L03 Counter top microwave | AppliancePartsPros.com

The Door Sense (Top) and Monitor (Middle) switches are supposed to be 15A NC microswitch. This switch have nothing to do with fixing mine but it is important to know just in case you want to replace them.

THEY ARE NOT THE SAME AS THE PRIMARY INTERLOCK SWITCH (15A NO switch posted by Jeff above). The parts list above, listed all switch with the same part no. (May be that part no. are for the switches with both NC and NO pins but I don't see both pins.) May be somebody can fix the part no to point to the correct one or follow the suggestion below. I know it is old models but it is still working fine and the inside components are probably still better quality than the one manufactured recently.

The best way if you are not sure about which switch to buy, get the one with both NC and NO pins. Cut the unnecessary pin. This saves time so you can take off the assembly and match it to the existing micro switches. Like this one:
Part Details - WHIRLPOOL Door interlock switch kit (2-pack), part number: AP3109474

I know this part is for Whirlpool but I it has the same functionality as the one for GE except with both pins (NC and NO). It is also a better deal. Cut the unnecessary pin. Sorry to Appliance Part Pros if this is not proper. Just a suggestion.

I ended up getting the micro switch with both pins to replace all the 3 switches although it was probably an overkill since I don't want to take the microwave out of the wall again, at least not in a short time. If you have a big box electronics store like Frys, it is available there as Philmore part no. 30-2000.

I have also found the manuals hidden inside the inner cavity of the microwave which can help you in the proper diagnostic.

The sign of a bad switch is when you press the switch, it does not have the clicking sound and feel loose, no spring feeling. If you don't want to get the Voltmeter out of the cabinet.

Glossary:
NO: Normally Open: door closed 0 ohm, door open is inf ohm.
NC: Normally Closed: door closed inf ohm, door open is 0 ohm.
inf: infinity.

I hope this can help somebody else.

Thanks for the direction from the Appliance Part Warehouse staff.

My microwave je1540wv002 recently started to have the same problem and came across this site. Microwave works fine but light on and turntable turns when door is open. Please advise which parts # to replace.

I have a GE Microwave model JVM1790SK01. Lately when I open the door the inside fan will start to work.